1<!--===- docs/Intrinsics.md 2 3 Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 See https://llvm.org/LICENSE.txt for license information. 5 SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 7--> 8 9# A categorization of standard (2018) and extended Fortran intrinsic procedures 10 11```{contents} 12--- 13local: 14--- 15``` 16 17This note attempts to group the intrinsic procedures of Fortran into categories 18of functions or subroutines with similar interfaces as an aid to 19comprehension beyond that which might be gained from the standard's 20alphabetical list. 21 22A brief status of intrinsic procedure support in f18 is also given at the end. 23 24Few procedures are actually described here apart from their interfaces; see the 25Fortran 2018 standard (section 16) for the complete story. 26 27Intrinsic modules are not covered here. 28 29## General rules 30 311. The value of any intrinsic function's `KIND` actual argument, if present, 32 must be a scalar constant integer expression, of any kind, whose value 33 resolves to some supported kind of the function's result type. 34 If optional and absent, the kind of the function's result is 35 either the default kind of that category or to the kind of an argument 36 (e.g., as in `AINT`). 371. Procedures are summarized with a non-Fortran syntax for brevity. 38 Wherever a function has a short definition, it appears after an 39 equal sign as if it were a statement function. Any functions referenced 40 in these short summaries are intrinsic. 411. Unless stated otherwise, an actual argument may have any supported kind 42 of a particular intrinsic type. Sometimes a pattern variable 43 can appear in a description (e.g., `REAL(k)`) when the kind of an 44 actual argument's type must match the kind of another argument, or 45 determines the kind type parameter of the function result. 461. When an intrinsic type name appears without a kind (e.g., `REAL`), 47 it refers to the default kind of that type. Sometimes the word 48 `default` will appear for clarity. 491. The names of the dummy arguments actually matter because they can 50 be used as keywords for actual arguments. 511. All standard intrinsic functions are pure, even when not elemental. 521. Assumed-rank arguments may not appear as actual arguments unless 53 expressly permitted. 541. When an argument is described with a default value, e.g. `KIND=KIND(0)`, 55 it is an optional argument. Optional arguments without defaults, 56 e.g. `DIM` on many transformationals, are wrapped in `[]` brackets 57 as in the Fortran standard. When an intrinsic has optional arguments 58 with and without default values, the arguments with default values 59 may appear within the brackets to preserve the order of arguments 60 (e.g., `COUNT`). 61 62## Elemental intrinsic functions 63 64Pure elemental semantics apply to these functions, to wit: when one or more of 65the actual arguments are arrays, the arguments must be conformable, and 66the result is also an array. 67Scalar arguments are expanded when the arguments are not all scalars. 68 69### Elemental intrinsic functions that may have unrestricted specific procedures 70 71When an elemental intrinsic function is documented here as having an 72_unrestricted specific name_, that name may be passed as an actual 73argument, used as the target of a procedure pointer, appear in 74a generic interface, and be otherwise used as if it were an external 75procedure. 76An `INTRINSIC` statement or attribute may have to be applied to an 77unrestricted specific name to enable such usage. 78 79When a name is being used as a specific procedure for any purpose other 80than that of a called function, the specific instance of the function 81that accepts and returns values of the default kinds of the intrinsic 82types is used. 83A Fortran `INTERFACE` could be written to define each of 84these unrestricted specific intrinsic function names. 85 86Calls to dummy arguments and procedure pointers that correspond to these 87specific names must pass only scalar actual argument values. 88 89No other intrinsic function name can be passed as an actual argument, 90used as a pointer target, appear in a generic interface, or be otherwise 91used except as the name of a called function. 92Some of these _restricted specific intrinsic functions_, e.g. `FLOAT`, 93provide a means for invoking a corresponding generic (`REAL` in the case of `FLOAT`) 94with forced argument and result kinds. 95Others, viz. `CHAR`, `ICHAR`, `INT`, `REAL`, and the lexical comparisons like `LGE`, 96have the same name as their generic functions, and it is not clear what purpose 97is accomplished by the standard by defining them as specific functions. 98 99### Trigonometric elemental intrinsic functions, generic and (mostly) specific 100All of these functions can be used as unrestricted specific names. 101 102``` 103ACOS(REAL(k) X) -> REAL(k) 104ASIN(REAL(k) X) -> REAL(k) 105ATAN(REAL(k) X) -> REAL(k) 106ATAN(REAL(k) Y, REAL(k) X) -> REAL(k) = ATAN2(Y, X) 107ATAN2(REAL(k) Y, REAL(k) X) -> REAL(k) 108COS(REAL(k) X) -> REAL(k) 109COSH(REAL(k) X) -> REAL(k) 110SIN(REAL(k) X) -> REAL(k) 111SINH(REAL(k) X) -> REAL(k) 112TAN(REAL(k) X) -> REAL(k) 113TANH(REAL(k) X) -> REAL(k) 114``` 115 116These `COMPLEX` versions of some of those functions, and the 117inverse hyperbolic functions, cannot be used as specific names. 118``` 119ACOS(COMPLEX(k) X) -> COMPLEX(k) 120ASIN(COMPLEX(k) X) -> COMPLEX(k) 121ATAN(COMPLEX(k) X) -> COMPLEX(k) 122ACOSH(REAL(k) X) -> REAL(k) 123ACOSH(COMPLEX(k) X) -> COMPLEX(k) 124ASINH(REAL(k) X) -> REAL(k) 125ASINH(COMPLEX(k) X) -> COMPLEX(k) 126ATANH(REAL(k) X) -> REAL(k) 127ATANH(COMPLEX(k) X) -> COMPLEX(k) 128COS(COMPLEX(k) X) -> COMPLEX(k) 129COSH(COMPLEX(k) X) -> COMPLEX(k) 130SIN(COMPLEX(k) X) -> COMPLEX(k) 131SINH(COMPLEX(k) X) -> COMPLEX(k) 132TAN(COMPLEX(k) X) -> COMPLEX(k) 133TANH(COMPLEX(k) X) -> COMPLEX(k) 134``` 135 136### Non-trigonometric elemental intrinsic functions, generic and specific 137These functions *can* be used as unrestricted specific names. 138``` 139ABS(REAL(k) A) -> REAL(k) = SIGN(A, 0.0) 140AIMAG(COMPLEX(k) Z) -> REAL(k) = Z%IM 141AINT(REAL(k) A, KIND=k) -> REAL(KIND) 142ANINT(REAL(k) A, KIND=k) -> REAL(KIND) 143CONJG(COMPLEX(k) Z) -> COMPLEX(k) = CMPLX(Z%RE, -Z%IM) 144DIM(REAL(k) X, REAL(k) Y) -> REAL(k) = X-MIN(X,Y) 145DPROD(default REAL X, default REAL Y) -> DOUBLE PRECISION = DBLE(X)*DBLE(Y) 146EXP(REAL(k) X) -> REAL(k) 147INDEX(CHARACTER(k) STRING, CHARACTER(k) SUBSTRING, LOGICAL(any) BACK=.FALSE., KIND=KIND(0)) -> INTEGER(KIND) 148LEN(CHARACTER(k,n) STRING, KIND=KIND(0)) -> INTEGER(KIND) = n 149LOG(REAL(k) X) -> REAL(k) 150LOG10(REAL(k) X) -> REAL(k) 151MOD(INTEGER(k) A, INTEGER(k) P) -> INTEGER(k) = A-P*INT(A/P) 152NINT(REAL(k) A, KIND=KIND(0)) -> INTEGER(KIND) 153SIGN(REAL(k) A, REAL(k) B) -> REAL(k) 154SQRT(REAL(k) X) -> REAL(k) = X ** 0.5 155``` 156 157These variants, however *cannot* be used as specific names without recourse to an alias 158from the following section: 159``` 160ABS(INTEGER(k) A) -> INTEGER(k) = SIGN(A, 0) 161ABS(COMPLEX(k) A) -> REAL(k) = HYPOT(A%RE, A%IM) 162DIM(INTEGER(k) X, INTEGER(k) Y) -> INTEGER(k) = X-MIN(X,Y) 163EXP(COMPLEX(k) X) -> COMPLEX(k) 164LOG(COMPLEX(k) X) -> COMPLEX(k) 165MOD(REAL(k) A, REAL(k) P) -> REAL(k) = A-P*INT(A/P) 166SIGN(INTEGER(k) A, INTEGER(k) B) -> INTEGER(k) 167SQRT(COMPLEX(k) X) -> COMPLEX(k) 168``` 169 170### Unrestricted specific aliases for some elemental intrinsic functions with distinct names 171 172``` 173ALOG(REAL X) -> REAL = LOG(X) 174ALOG10(REAL X) -> REAL = LOG10(X) 175AMOD(REAL A, REAL P) -> REAL = MOD(A, P) 176CABS(COMPLEX A) = ABS(A) 177CCOS(COMPLEX X) = COS(X) 178CEXP(COMPLEX A) -> COMPLEX = EXP(A) 179CLOG(COMPLEX X) -> COMPLEX = LOG(X) 180CSIN(COMPLEX X) -> COMPLEX = SIN(X) 181CSQRT(COMPLEX X) -> COMPLEX = SQRT(X) 182CTAN(COMPLEX X) -> COMPLEX = TAN(X) 183DABS(DOUBLE PRECISION A) -> DOUBLE PRECISION = ABS(A) 184DACOS(DOUBLE PRECISION X) -> DOUBLE PRECISION = ACOS(X) 185DASIN(DOUBLE PRECISION X) -> DOUBLE PRECISION = ASIN(X) 186DATAN(DOUBLE PRECISION X) -> DOUBLE PRECISION = ATAN(X) 187DATAN2(DOUBLE PRECISION Y, DOUBLE PRECISION X) -> DOUBLE PRECISION = ATAN2(Y, X) 188DCOS(DOUBLE PRECISION X) -> DOUBLE PRECISION = COS(X) 189DCOSH(DOUBLE PRECISION X) -> DOUBLE PRECISION = COSH(X) 190DDIM(DOUBLE PRECISION X, DOUBLE PRECISION Y) -> DOUBLE PRECISION = X-MIN(X,Y) 191DEXP(DOUBLE PRECISION X) -> DOUBLE PRECISION = EXP(X) 192DINT(DOUBLE PRECISION A) -> DOUBLE PRECISION = AINT(A) 193DLOG(DOUBLE PRECISION X) -> DOUBLE PRECISION = LOG(X) 194DLOG10(DOUBLE PRECISION X) -> DOUBLE PRECISION = LOG10(X) 195DMOD(DOUBLE PRECISION A, DOUBLE PRECISION P) -> DOUBLE PRECISION = MOD(A, P) 196DNINT(DOUBLE PRECISION A) -> DOUBLE PRECISION = ANINT(A) 197DSIGN(DOUBLE PRECISION A, DOUBLE PRECISION B) -> DOUBLE PRECISION = SIGN(A, B) 198DSIN(DOUBLE PRECISION X) -> DOUBLE PRECISION = SIN(X) 199DSINH(DOUBLE PRECISION X) -> DOUBLE PRECISION = SINH(X) 200DSQRT(DOUBLE PRECISION X) -> DOUBLE PRECISION = SQRT(X) 201DTAN(DOUBLE PRECISION X) -> DOUBLE PRECISION = TAN(X) 202DTANH(DOUBLE PRECISION X) -> DOUBLE PRECISION = TANH(X) 203IABS(INTEGER A) -> INTEGER = ABS(A) 204IDIM(INTEGER X, INTEGER Y) -> INTEGER = X-MIN(X,Y) 205IDNINT(DOUBLE PRECISION A) -> INTEGER = NINT(A) 206ISIGN(INTEGER A, INTEGER B) -> INTEGER = SIGN(A, B) 207``` 208 209## Generic elemental intrinsic functions without specific names 210 211(No procedures after this point can be passed as actual arguments, used as 212pointer targets, or appear as specific procedures in generic interfaces.) 213 214### Elemental conversions 215 216``` 217ACHAR(INTEGER(k) I, KIND=KIND('')) -> CHARACTER(KIND,LEN=1) 218CEILING(REAL() A, KIND=KIND(0)) -> INTEGER(KIND) 219CHAR(INTEGER(any) I, KIND=KIND('')) -> CHARACTER(KIND,LEN=1) 220CMPLX(COMPLEX(k) X, KIND=KIND(0.0D0)) -> COMPLEX(KIND) 221CMPLX(INTEGER or REAL or BOZ X, INTEGER or REAL or BOZ Y=0, KIND=KIND((0,0))) -> COMPLEX(KIND) 222DBLE(INTEGER or REAL or COMPLEX or BOZ A) = REAL(A, KIND=KIND(0.0D0)) 223EXPONENT(REAL(any) X) -> default INTEGER 224FLOOR(REAL(any) A, KIND=KIND(0)) -> INTEGER(KIND) 225IACHAR(CHARACTER(KIND=k,LEN=1) C, KIND=KIND(0)) -> INTEGER(KIND) 226ICHAR(CHARACTER(KIND=k,LEN=1) C, KIND=KIND(0)) -> INTEGER(KIND) 227INT(INTEGER or REAL or COMPLEX or BOZ A, KIND=KIND(0)) -> INTEGER(KIND) 228LOGICAL(LOGICAL(any) L, KIND=KIND(.TRUE.)) -> LOGICAL(KIND) 229REAL(INTEGER or REAL or COMPLEX or BOZ A, KIND=KIND(0.0)) -> REAL(KIND) 230``` 231 232### Other generic elemental intrinsic functions without specific names 233N.B. `BESSEL_JN(N1, N2, X)` and `BESSEL_YN(N1, N2, X)` are categorized 234below with the _transformational_ intrinsic functions. 235 236``` 237BESSEL_J0(REAL(k) X) -> REAL(k) 238BESSEL_J1(REAL(k) X) -> REAL(k) 239BESSEL_JN(INTEGER(n) N, REAL(k) X) -> REAL(k) 240BESSEL_Y0(REAL(k) X) -> REAL(k) 241BESSEL_Y1(REAL(k) X) -> REAL(k) 242BESSEL_YN(INTEGER(n) N, REAL(k) X) -> REAL(k) 243ERF(REAL(k) X) -> REAL(k) 244ERFC(REAL(k) X) -> REAL(k) 245ERFC_SCALED(REAL(k) X) -> REAL(k) 246FRACTION(REAL(k) X) -> REAL(k) 247GAMMA(REAL(k) X) -> REAL(k) 248HYPOT(REAL(k) X, REAL(k) Y) -> REAL(k) = SQRT(X*X+Y*Y) without spurious overflow 249IMAGE_STATUS(INTEGER(any) IMAGE [, scalar TEAM_TYPE TEAM ]) -> default INTEGER 250IS_IOSTAT_END(INTEGER(any) I) -> default LOGICAL 251IS_IOSTAT_EOR(INTEGER(any) I) -> default LOGICAL 252LOG_GAMMA(REAL(k) X) -> REAL(k) 253MAX(INTEGER(k) ...) -> INTEGER(k) 254MAX(REAL(k) ...) -> REAL(k) 255MAX(CHARACTER(KIND=k) ...) -> CHARACTER(KIND=k,LEN=MAX(LEN(...))) 256MERGE(any type TSOURCE, same type FSOURCE, LOGICAL(any) MASK) -> type of FSOURCE 257MIN(INTEGER(k) ...) -> INTEGER(k) 258MIN(REAL(k) ...) -> REAL(k) 259MIN(CHARACTER(KIND=k) ...) -> CHARACTER(KIND=k,LEN=MAX(LEN(...))) 260MODULO(INTEGER(k) A, INTEGER(k) P) -> INTEGER(k); P*result >= 0 261MODULO(REAL(k) A, REAL(k) P) -> REAL(k) = A - P*FLOOR(A/P) 262NEAREST(REAL(k) X, REAL(any) S) -> REAL(k) 263OUT_OF_RANGE(INTEGER(any) X, scalar INTEGER or REAL(k) MOLD) -> default LOGICAL 264OUT_OF_RANGE(REAL(any) X, scalar REAL(k) MOLD) -> default LOGICAL 265OUT_OF_RANGE(REAL(any) X, scalar INTEGER(any) MOLD, scalar LOGICAL(any) ROUND=.FALSE.) -> default LOGICAL 266RRSPACING(REAL(k) X) -> REAL(k) 267SCALE(REAL(k) X, INTEGER(any) I) -> REAL(k) 268SET_EXPONENT(REAL(k) X, INTEGER(any) I) -> REAL(k) 269SPACING(REAL(k) X) -> REAL(k) 270``` 271 272### Restricted specific aliases for elemental conversions &/or extrema with default intrinsic types 273 274``` 275AMAX0(INTEGER ...) = REAL(MAX(...)) 276AMAX1(REAL ...) = MAX(...) 277AMIN0(INTEGER...) = REAL(MIN(...)) 278AMIN1(REAL ...) = MIN(...) 279DMAX1(DOUBLE PRECISION ...) = MAX(...) 280DMIN1(DOUBLE PRECISION ...) = MIN(...) 281FLOAT(INTEGER I) = REAL(I) 282IDINT(DOUBLE PRECISION A) = INT(A) 283IFIX(REAL A) = INT(A) 284MAX0(INTEGER ...) = MAX(...) 285MAX1(REAL ...) = INT(MAX(...)) 286MIN0(INTEGER ...) = MIN(...) 287MIN1(REAL ...) = INT(MIN(...)) 288SNGL(DOUBLE PRECISION A) = REAL(A) 289``` 290 291### Generic elemental bit manipulation intrinsic functions 292Many of these accept a typeless "BOZ" literal as an actual argument. 293It is interpreted as having the kind of intrinsic `INTEGER` type 294as another argument, as if the typeless were implicitly wrapped 295in a call to `INT()`. 296When multiple arguments can be either `INTEGER` values or typeless 297constants, it is forbidden for *all* of them to be typeless 298constants if the result of the function is `INTEGER` 299(i.e., only `BGE`, `BGT`, `BLE`, and `BLT` can have multiple 300typeless arguments). 301 302``` 303BGE(INTEGER(n1) or BOZ I, INTEGER(n2) or BOZ J) -> default LOGICAL 304BGT(INTEGER(n1) or BOZ I, INTEGER(n2) or BOZ J) -> default LOGICAL 305BLE(INTEGER(n1) or BOZ I, INTEGER(n2) or BOZ J) -> default LOGICAL 306BLT(INTEGER(n1) or BOZ I, INTEGER(n2) or BOZ J) -> default LOGICAL 307BTEST(INTEGER(n1) I, INTEGER(n2) POS) -> default LOGICAL 308DSHIFTL(INTEGER(k) I, INTEGER(k) or BOZ J, INTEGER(any) SHIFT) -> INTEGER(k) 309DSHIFTL(BOZ I, INTEGER(k), INTEGER(any) SHIFT) -> INTEGER(k) 310DSHIFTR(INTEGER(k) I, INTEGER(k) or BOZ J, INTEGER(any) SHIFT) -> INTEGER(k) 311DSHIFTR(BOZ I, INTEGER(k), INTEGER(any) SHIFT) -> INTEGER(k) 312IAND(INTEGER(k) I, INTEGER(k) or BOZ J) -> INTEGER(k) 313IAND(BOZ I, INTEGER(k) J) -> INTEGER(k) 314IBCLR(INTEGER(k) I, INTEGER(any) POS) -> INTEGER(k) 315IBITS(INTEGER(k) I, INTEGER(n1) POS, INTEGER(n2) LEN) -> INTEGER(k) 316IBSET(INTEGER(k) I, INTEGER(any) POS) -> INTEGER(k) 317IEOR(INTEGER(k) I, INTEGER(k) or BOZ J) -> INTEGER(k) 318IEOR(BOZ I, INTEGER(k) J) -> INTEGER(k) 319IOR(INTEGER(k) I, INTEGER(k) or BOZ J) -> INTEGER(k) 320IOR(BOZ I, INTEGER(k) J) -> INTEGER(k) 321ISHFT(INTEGER(k) I, INTEGER(any) SHIFT) -> INTEGER(k) 322ISHFTC(INTEGER(k) I, INTEGER(n1) SHIFT, INTEGER(n2) SIZE=BIT_SIZE(I)) -> INTEGER(k) 323LEADZ(INTEGER(any) I) -> default INTEGER 324MASKL(INTEGER(any) I, KIND=KIND(0)) -> INTEGER(KIND) 325MASKR(INTEGER(any) I, KIND=KIND(0)) -> INTEGER(KIND) 326MERGE_BITS(INTEGER(k) I, INTEGER(k) or BOZ J, INTEGER(k) or BOZ MASK) = IOR(IAND(I,MASK),IAND(J,NOT(MASK))) 327MERGE_BITS(BOZ I, INTEGER(k) J, INTEGER(k) or BOZ MASK) = IOR(IAND(I,MASK),IAND(J,NOT(MASK))) 328NOT(INTEGER(k) I) -> INTEGER(k) 329POPCNT(INTEGER(any) I) -> default INTEGER 330POPPAR(INTEGER(any) I) -> default INTEGER = IAND(POPCNT(I), Z'1') 331SHIFTA(INTEGER(k) I, INTEGER(any) SHIFT) -> INTEGER(k) 332SHIFTL(INTEGER(k) I, INTEGER(any) SHIFT) -> INTEGER(k) 333SHIFTR(INTEGER(k) I, INTEGER(any) SHIFT) -> INTEGER(k) 334TRAILZ(INTEGER(any) I) -> default INTEGER 335``` 336 337### Character elemental intrinsic functions 338See also `INDEX` and `LEN` above among the elemental intrinsic functions with 339unrestricted specific names. 340``` 341ADJUSTL(CHARACTER(k,LEN=n) STRING) -> CHARACTER(k,LEN=n) 342ADJUSTR(CHARACTER(k,LEN=n) STRING) -> CHARACTER(k,LEN=n) 343LEN_TRIM(CHARACTER(k,n) STRING, KIND=KIND(0)) -> INTEGER(KIND) = n 344LGE(CHARACTER(k,n1) STRING_A, CHARACTER(k,n2) STRING_B) -> default LOGICAL 345LGT(CHARACTER(k,n1) STRING_A, CHARACTER(k,n2) STRING_B) -> default LOGICAL 346LLE(CHARACTER(k,n1) STRING_A, CHARACTER(k,n2) STRING_B) -> default LOGICAL 347LLT(CHARACTER(k,n1) STRING_A, CHARACTER(k,n2) STRING_B) -> default LOGICAL 348SCAN(CHARACTER(k,n) STRING, CHARACTER(k,m) SET, LOGICAL(any) BACK=.FALSE., KIND=KIND(0)) -> INTEGER(KIND) 349VERIFY(CHARACTER(k,n) STRING, CHARACTER(k,m) SET, LOGICAL(any) BACK=.FALSE., KIND=KIND(0)) -> INTEGER(KIND) 350``` 351 352`SCAN` returns the index of the first (or last, if `BACK=.TRUE.`) character in `STRING` 353that is present in `SET`, or zero if none is. 354 355`VERIFY` is essentially the opposite: it returns the index of the first (or last) character 356in `STRING` that is *not* present in `SET`, or zero if all are. 357 358## Transformational intrinsic functions 359 360This category comprises a large collection of intrinsic functions that 361are collected together because they somehow transform their arguments 362in a way that prevents them from being elemental. 363All of them are pure, however. 364 365Some general rules apply to the transformational intrinsic functions: 366 3671. `DIM` arguments are optional; if present, the actual argument must be 368 a scalar integer of any kind. 3691. When an optional `DIM` argument is absent, or an `ARRAY` or `MASK` 370 argument is a vector, the result of the function is scalar; otherwise, 371 the result is an array of the same shape as the `ARRAY` or `MASK` 372 argument with the dimension `DIM` removed from the shape. 3731. When a function takes an optional `MASK` argument, it must be conformable 374 with its `ARRAY` argument if it is present, and the mask can be any kind 375 of `LOGICAL`. It can be scalar. 3761. The type `numeric` here can be any kind of `INTEGER`, `REAL`, or `COMPLEX`. 3771. The type `relational` here can be any kind of `INTEGER`, `REAL`, or `CHARACTER`. 3781. The type `any` here denotes any intrinsic or derived type. 3791. The notation `(..)` denotes an array of any rank (but not an assumed-rank array). 380 381### Logical reduction transformational intrinsic functions 382``` 383ALL(LOGICAL(k) MASK(..) [, DIM ]) -> LOGICAL(k) 384ANY(LOGICAL(k) MASK(..) [, DIM ]) -> LOGICAL(k) 385COUNT(LOGICAL(any) MASK(..) [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 386PARITY(LOGICAL(k) MASK(..) [, DIM ]) -> LOGICAL(k) 387``` 388 389### Numeric reduction transformational intrinsic functions 390``` 391IALL(INTEGER(k) ARRAY(..) [, DIM, MASK ]) -> INTEGER(k) 392IANY(INTEGER(k) ARRAY(..) [, DIM, MASK ]) -> INTEGER(k) 393IPARITY(INTEGER(k) ARRAY(..) [, DIM, MASK ]) -> INTEGER(k) 394NORM2(REAL(k) X(..) [, DIM ]) -> REAL(k) 395PRODUCT(numeric ARRAY(..) [, DIM, MASK ]) -> numeric 396SUM(numeric ARRAY(..) [, DIM, MASK ]) -> numeric 397``` 398 399`NORM2` generalizes `HYPOT` by computing `SQRT(SUM(X*X))` while avoiding spurious overflows. 400 401### Extrema reduction transformational intrinsic functions 402``` 403MAXVAL(relational(k) ARRAY(..) [, DIM, MASK ]) -> relational(k) 404MINVAL(relational(k) ARRAY(..) [, DIM, MASK ]) -> relational(k) 405``` 406 407### Locational transformational intrinsic functions 408When the optional `DIM` argument is absent, the result is an `INTEGER(KIND)` 409vector whose length is the rank of `ARRAY`. 410When the optional `DIM` argument is present, the result is an `INTEGER(KIND)` 411array of rank `RANK(ARRAY)-1` and shape equal to that of `ARRAY` with 412the dimension `DIM` removed. 413 414The optional `BACK` argument is a scalar LOGICAL value of any kind. 415When present and `.TRUE.`, it causes the function to return the index 416of the *last* occurence of the target or extreme value. 417 418For `FINDLOC`, `ARRAY` may have any of the five intrinsic types, and `VALUE` 419must a scalar value of a type for which `ARRAY==VALUE` or `ARRAY .EQV. VALUE` 420is an acceptable expression. 421 422``` 423FINDLOC(intrinsic ARRAY(..), scalar VALUE [, DIM, MASK, KIND=KIND(0), BACK=.FALSE. ]) 424MAXLOC(relational ARRAY(..) [, DIM, MASK, KIND=KIND(0), BACK=.FALSE. ]) 425MINLOC(relational ARRAY(..) [, DIM, MASK, KIND=KIND(0), BACK=.FALSE. ]) 426``` 427 428### Data rearrangement transformational intrinsic functions 429The optional `DIM` argument to these functions must be a scalar integer of 430any kind, and it takes a default value of 1 when absent. 431 432``` 433CSHIFT(any ARRAY(..), INTEGER(any) SHIFT(..) [, DIM ]) -> same type/kind/shape as ARRAY 434``` 435Either `SHIFT` is scalar or `RANK(SHIFT) == RANK(ARRAY) - 1` and `SHAPE(SHIFT)` is that of `SHAPE(ARRAY)` with element `DIM` removed. 436 437``` 438EOSHIFT(any ARRAY(..), INTEGER(any) SHIFT(..) [, BOUNDARY, DIM ]) -> same type/kind/shape as ARRAY 439``` 440* `SHIFT` is scalar or `RANK(SHIFT) == RANK(ARRAY) - 1` and `SHAPE(SHIFT)` is that of `SHAPE(ARRAY)` with element `DIM` removed. 441* If `BOUNDARY` is present, it must have the same type and parameters as `ARRAY`. 442* If `BOUNDARY` is absent, `ARRAY` must be of an intrinsic type, and the default `BOUNDARY` is the obvious `0`, `' '`, or `.FALSE.` value of `KIND(ARRAY)`. 443* If `BOUNDARY` is present, either it is scalar, or `RANK(BOUNDARY) == RANK(ARRAY) - 1` and `SHAPE(BOUNDARY)` is that of `SHAPE(ARRAY)` with element `DIM` 444 removed. 445 446``` 447PACK(any ARRAY(..), LOGICAL(any) MASK(..)) -> vector of same type and kind as ARRAY 448``` 449* `MASK` is conformable with `ARRAY` and may be scalar. 450* The length of the result vector is `COUNT(MASK)` if `MASK` is an array, else `SIZE(ARRAY)` if `MASK` is `.TRUE.`, else zero. 451 452``` 453PACK(any ARRAY(..), LOGICAL(any) MASK(..), any VECTOR(n)) -> vector of same type, kind, and size as VECTOR 454``` 455* `MASK` is conformable with `ARRAY` and may be scalar. 456* `VECTOR` has the same type and kind as `ARRAY`. 457* `VECTOR` must not be smaller than result of `PACK` with no `VECTOR` argument. 458* The leading elements of `VECTOR` are replaced with elements from `ARRAY` as 459 if `PACK` had been invoked without `VECTOR`. 460 461``` 462RESHAPE(any SOURCE(..), INTEGER(k) SHAPE(n) [, PAD(..), INTEGER(k2) ORDER(n) ]) -> SOURCE array with shape SHAPE 463``` 464* If `ORDER` is present, it is a vector of the same size as `SHAPE`, and 465 contains a permutation. 466* The element(s) of `PAD` are used to fill out the result once `SOURCE` 467 has been consumed. 468 469``` 470SPREAD(any SOURCE, DIM, scalar INTEGER(any) NCOPIES) -> same type as SOURCE, rank=RANK(SOURCE)+1 471TRANSFER(any SOURCE, any MOLD) -> scalar if MOLD is scalar, else vector; same type and kind as MOLD 472TRANSFER(any SOURCE, any MOLD, scalar INTEGER(any) SIZE) -> vector(SIZE) of type and kind of MOLD 473TRANSPOSE(any MATRIX(n,m)) -> matrix(m,n) of same type and kind as MATRIX 474``` 475 476The shape of the result of `SPREAD` is the same as that of `SOURCE`, with `NCOPIES` inserted 477at position `DIM`. 478 479``` 480UNPACK(any VECTOR(n), LOGICAL(any) MASK(..), FIELD) -> type and kind of VECTOR, shape of MASK 481``` 482`FIELD` has same type and kind as `VECTOR` and is conformable with `MASK`. 483 484### Other transformational intrinsic functions 485``` 486BESSEL_JN(INTEGER(n1) N1, INTEGER(n2) N2, REAL(k) X) -> REAL(k) vector (MAX(N2-N1+1,0)) 487BESSEL_YN(INTEGER(n1) N1, INTEGER(n2) N2, REAL(k) X) -> REAL(k) vector (MAX(N2-N1+1,0)) 488COMMAND_ARGUMENT_COUNT() -> scalar default INTEGER 489DOT_PRODUCT(LOGICAL(k) VECTOR_A(n), LOGICAL(k) VECTOR_B(n)) -> LOGICAL(k) = ANY(VECTOR_A .AND. VECTOR_B) 490DOT_PRODUCT(COMPLEX(any) VECTOR_A(n), numeric VECTOR_B(n)) = SUM(CONJG(VECTOR_A) * VECTOR_B) 491DOT_PRODUCT(INTEGER(any) or REAL(any) VECTOR_A(n), numeric VECTOR_B(n)) = SUM(VECTOR_A * VECTOR_B) 492MATMUL(numeric ARRAY_A(j), numeric ARRAY_B(j,k)) -> numeric vector(k) 493MATMUL(numeric ARRAY_A(j,k), numeric ARRAY_B(k)) -> numeric vector(j) 494MATMUL(numeric ARRAY_A(j,k), numeric ARRAY_B(k,m)) -> numeric matrix(j,m) 495MATMUL(LOGICAL(n1) ARRAY_A(j), LOGICAL(n2) ARRAY_B(j,k)) -> LOGICAL vector(k) 496MATMUL(LOGICAL(n1) ARRAY_A(j,k), LOGICAL(n2) ARRAY_B(k)) -> LOGICAL vector(j) 497MATMUL(LOGICAL(n1) ARRAY_A(j,k), LOGICAL(n2) ARRAY_B(k,m)) -> LOGICAL matrix(j,m) 498NULL([POINTER/ALLOCATABLE MOLD]) -> POINTER 499REDUCE(any ARRAY(..), function OPERATION [, DIM, LOGICAL(any) MASK(..), IDENTITY, LOGICAL ORDERED=.FALSE. ]) 500REPEAT(CHARACTER(k,n) STRING, INTEGER(any) NCOPIES) -> CHARACTER(k,n*NCOPIES) 501SELECTED_CHAR_KIND('DEFAULT' or 'ASCII' or 'ISO_10646' or ...) -> scalar default INTEGER 502SELECTED_INT_KIND(scalar INTEGER(any) R) -> scalar default INTEGER 503SELECTED_REAL_KIND([scalar INTEGER(any) P, scalar INTEGER(any) R, scalar INTEGER(any) RADIX]) -> scalar default INTEGER 504SHAPE(SOURCE, KIND=KIND(0)) -> INTEGER(KIND)(RANK(SOURCE)) 505TRIM(CHARACTER(k,n) STRING) -> CHARACTER(k) 506``` 507 508The type and kind of the result of a numeric `MATMUL` is the same as would result from 509a multiplication of an element of ARRAY_A and an element of ARRAY_B. 510 511The kind of the `LOGICAL` result of a `LOGICAL` `MATMUL` is the same as would result 512from an intrinsic `.AND.` operation between an element of `ARRAY_A` and an element 513of `ARRAY_B`. 514 515Note that `DOT_PRODUCT` with a `COMPLEX` first argument operates on its complex conjugate, 516but that `MATMUL` with a `COMPLEX` argument does not. 517 518The `MOLD` argument to `NULL` may be omitted only in a context where the type of the pointer is known, 519such as an initializer or pointer assignment statement. 520 521At least one argument must be present in a call to `SELECTED_REAL_KIND`. 522 523An assumed-rank array may be passed to `SHAPE`, and if it is associated with an assumed-size array, 524the last element of the result will be -1. 525 526### Coarray transformational intrinsic functions 527``` 528FAILED_IMAGES([scalar TEAM_TYPE TEAM, KIND=KIND(0)]) -> INTEGER(KIND) vector 529GET_TEAM([scalar INTEGER(?) LEVEL]) -> scalar TEAM_TYPE 530IMAGE_INDEX(COARRAY, INTEGER(any) SUB(n) [, scalar TEAM_TYPE TEAM ]) -> scalar default INTEGER 531IMAGE_INDEX(COARRAY, INTEGER(any) SUB(n), scalar INTEGER(any) TEAM_NUMBER) -> scalar default INTEGER 532NUM_IMAGES([scalar TEAM_TYPE TEAM]) -> scalar default INTEGER 533NUM_IMAGES(scalar INTEGER(any) TEAM_NUMBER) -> scalar default INTEGER 534STOPPED_IMAGES([scalar TEAM_TYPE TEAM, KIND=KIND(0)]) -> INTEGER(KIND) vector 535TEAM_NUMBER([scalar TEAM_TYPE TEAM]) -> scalar default INTEGER 536THIS_IMAGE([COARRAY, DIM, scalar TEAM_TYPE TEAM]) -> default INTEGER 537``` 538The result of `THIS_IMAGE` is a scalar if `DIM` is present or if `COARRAY` is absent, 539and a vector whose length is the corank of `COARRAY` otherwise. 540 541## Inquiry intrinsic functions 542These are neither elemental nor transformational; all are pure. 543 544### Type inquiry intrinsic functions 545All of these functions return constants. 546The value of the argument is not used, and may well be undefined. 547``` 548BIT_SIZE(INTEGER(k) I(..)) -> INTEGER(k) 549DIGITS(INTEGER or REAL X(..)) -> scalar default INTEGER 550EPSILON(REAL(k) X(..)) -> scalar REAL(k) 551HUGE(INTEGER(k) X(..)) -> scalar INTEGER(k) 552HUGE(REAL(k) X(..)) -> scalar of REAL(k) 553KIND(intrinsic X(..)) -> scalar default INTEGER 554MAXEXPONENT(REAL(k) X(..)) -> scalar default INTEGER 555MINEXPONENT(REAL(k) X(..)) -> scalar default INTEGER 556NEW_LINE(CHARACTER(k,n) A(..)) -> scalar CHARACTER(k,1) = CHAR(10) 557PRECISION(REAL(k) or COMPLEX(k) X(..)) -> scalar default INTEGER 558RADIX(INTEGER(k) or REAL(k) X(..)) -> scalar default INTEGER, always 2 559RANGE(INTEGER(k) or REAL(k) or COMPLEX(k) X(..)) -> scalar default INTEGER 560TINY(REAL(k) X(..)) -> scalar REAL(k) 561``` 562 563### Bound and size inquiry intrinsic functions 564The results are scalar when `DIM` is present, and a vector of length=(co)rank(`(CO)ARRAY`) 565when `DIM` is absent. 566``` 567LBOUND(any ARRAY(..) [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 568LCOBOUND(any COARRAY [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 569SIZE(any ARRAY(..) [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 570UBOUND(any ARRAY(..) [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 571UCOBOUND(any COARRAY [, DIM, KIND=KIND(0) ]) -> INTEGER(KIND) 572``` 573 574Assumed-rank arrays may be used with `LBOUND`, `SIZE`, and `UBOUND`. 575 576### Object characteristic inquiry intrinsic functions 577``` 578ALLOCATED(any type ALLOCATABLE ARRAY) -> scalar default LOGICAL 579ALLOCATED(any type ALLOCATABLE SCALAR) -> scalar default LOGICAL 580ASSOCIATED(any type POINTER POINTER [, same type TARGET]) -> scalar default LOGICAL 581COSHAPE(COARRAY, KIND=KIND(0)) -> INTEGER(KIND) vector of length corank(COARRAY) 582EXTENDS_TYPE_OF(A, MOLD) -> default LOGICAL 583IS_CONTIGUOUS(any data ARRAY(..)) -> scalar default LOGICAL 584PRESENT(OPTIONAL A) -> scalar default LOGICAL 585RANK(any data A) -> scalar default INTEGER = 0 if A is scalar, SIZE(SHAPE(A)) if A is an array, rank if assumed-rank 586SAME_TYPE_AS(A, B) -> scalar default LOGICAL 587STORAGE_SIZE(any data A, KIND=KIND(0)) -> INTEGER(KIND) 588``` 589The arguments to `EXTENDS_TYPE_OF` must be of extensible derived types or be unlimited polymorphic. 590 591An assumed-rank array may be used with `IS_CONTIGUOUS` and `RANK`. 592 593## Intrinsic subroutines 594 595(*TODO*: complete these descriptions) 596 597### One elemental intrinsic subroutine 598``` 599INTERFACE 600 SUBROUTINE MVBITS(FROM, FROMPOS, LEN, TO, TOPOS) 601 INTEGER(k1) :: FROM, TO 602 INTENT(IN) :: FROM 603 INTENT(INOUT) :: TO 604 INTEGER(k2), INTENT(IN) :: FROMPOS 605 INTEGER(k3), INTENT(IN) :: LEN 606 INTEGER(k4), INTENT(IN) :: TOPOS 607 END SUBROUTINE 608END INTERFACE 609``` 610 611### Non-elemental intrinsic subroutines 612``` 613CALL CPU_TIME(REAL INTENT(OUT) TIME) 614``` 615The kind of `TIME` is not specified in the standard. 616 617``` 618CALL DATE_AND_TIME([DATE, TIME, ZONE, VALUES]) 619``` 620* All arguments are `OPTIONAL` and `INTENT(OUT)`. 621* `DATE`, `TIME`, and `ZONE` are scalar default `CHARACTER`. 622* `VALUES` is a vector of at least 8 elements of `INTEGER(KIND >= 2)`. 623``` 624CALL EVENT_QUERY(EVENT, COUNT [, STAT]) 625CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT, CMDMSG ]) 626CALL GET_COMMAND([COMMAND, LENGTH, STATUS, ERRMSG ]) 627CALL GET_COMMAND_ARGUMENT(NUMBER [, VALUE, LENGTH, STATUS, ERRMSG ]) 628CALL GET_ENVIRONMENT_VARIABLE(NAME [, VALUE, LENGTH, STATUS, TRIM_NAME, ERRMSG ]) 629CALL MOVE_ALLOC(ALLOCATABLE INTENT(INOUT) FROM, ALLOCATABLE INTENT(OUT) TO [, STAT, ERRMSG ]) 630CALL RANDOM_INIT(LOGICAL(k1) INTENT(IN) REPEATABLE, LOGICAL(k2) INTENT(IN) IMAGE_DISTINCT) 631CALL RANDOM_NUMBER(REAL(k) INTENT(OUT) HARVEST(..)) 632CALL RANDOM_SEED([SIZE, PUT, GET]) 633CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX]) 634``` 635 636### Atomic intrinsic subroutines 637``` 638CALL ATOMIC_ADD(ATOM, VALUE [, STAT=]) 639CALL ATOMIC_AND(ATOM, VALUE [, STAT=]) 640CALL ATOMIC_CAS(ATOM, OLD, COMPARE, NEW [, STAT=]) 641CALL ATOMIC_DEFINE(ATOM, VALUE [, STAT=]) 642CALL ATOMIC_FETCH_ADD(ATOM, VALUE, OLD [, STAT=]) 643CALL ATOMIC_FETCH_AND(ATOM, VALUE, OLD [, STAT=]) 644CALL ATOMIC_FETCH_OR(ATOM, VALUE, OLD [, STAT=]) 645CALL ATOMIC_FETCH_XOR(ATOM, VALUE, OLD [, STAT=]) 646CALL ATOMIC_OR(ATOM, VALUE [, STAT=]) 647CALL ATOMIC_REF(VALUE, ATOM [, STAT=]) 648CALL ATOMIC_XOR(ATOM, VALUE [, STAT=]) 649``` 650 651### Collective intrinsic subroutines 652``` 653CALL CO_BROADCAST 654CALL CO_MAX 655CALL CO_MIN 656CALL CO_REDUCE 657CALL CO_SUM 658``` 659 660### Inquiry Functions 661ACCESS (GNU extension) is not supported on Windows. Otherwise: 662``` 663CHARACTER(LEN=*) :: path = 'path/to/file' 664IF (ACCESS(path, 'rwx')) & 665 ... 666``` 667 668## Non-standard intrinsics 669### PGI 670``` 671AND, OR, XOR 672LSHIFT, RSHIFT, SHIFT 673ZEXT, IZEXT 674COSD, SIND, TAND, ACOSD, ASIND, ATAND, ATAN2D 675COMPL 676DCMPLX 677EQV, NEQV 678INT8 679JINT, JNINT, KNINT 680LOC 681``` 682 683### Intel 684``` 685DCMPLX(X,Y), QCMPLX(X,Y) 686DREAL(DOUBLE COMPLEX A) -> DOUBLE PRECISION 687DFLOAT, DREAL 688QEXT, QFLOAT, QREAL 689DNUM, INUM, JNUM, KNUM, QNUM, RNUM - scan value from string 690ZEXT 691RAN, RANF 692ILEN(I) = BIT_SIZE(I) 693SIZEOF 694MCLOCK, SECNDS 695COTAN(X) = 1.0/TAN(X) 696COSD, SIND, TAND, ACOSD, ASIND, ATAND, ATAN2D, COTAND - degrees 697AND, OR, XOR 698LSHIFT, RSHIFT 699IBCHNG, ISHA, ISHC, ISHL, IXOR 700IARG, IARGC, NARGS, NUMARG 701BADDRESS, IADDR 702CACHESIZE, EOF, FP_CLASS, INT_PTR_KIND, ISNAN, LOC 703MALLOC, FREE 704``` 705 706### Library subroutine 707``` 708CALL BACKTRACE() 709CALL FDATE(TIME) 710CALL GETLOG(USRNAME) 711CALL GETENV(NAME [, VALUE, LENGTH, STATUS, TRIM_NAME, ERRMSG ]) 712``` 713 714## Intrinsic Procedure Name Resolution 715 716When the name of a procedure in a program is the same as the one of an intrinsic 717procedure, and nothing other than its usage allows to decide whether the procedure 718is the intrinsic or not (i.e, it does not appear in an INTRINSIC or EXTERNAL attribute 719statement, is not an use/host associated procedure...), Fortran 2018 standard 720section 19.5.1.4 point 6 rules that the procedure is established to be intrinsic if it is 721invoked as an intrinsic procedure. 722 723In case the invocation would be an error if the procedure were the intrinsic 724(e.g. wrong argument number or type), the broad wording of the standard 725leaves two choices to the compiler: emit an error about the intrinsic invocation, 726or consider this is an external procedure and emit no error. 727 728f18 will always consider this case to be the intrinsic and emit errors, unless the procedure 729is used as a function (resp. subroutine) and the intrinsic is a subroutine (resp. function). 730The table below gives some examples of decisions made by Fortran compilers in such case. 731 732| What is ACOS ? | Bad intrinsic call | External with warning | External no warning | Other error | 733| --- | --- | --- | --- | --- | 734| `print*, ACOS()` | gfortran, nag, xlf, f18 | ifort | nvfortran | | 735| `print*, ACOS(I)` | gfortran, nag, xlf, f18 | ifort | nvfortran | | 736| `print*, ACOS(X=I)` | gfortran, nag, xlf, f18 | ifort | | nvfortran (keyword on implicit extrenal )| 737| `print*, ACOS(X, X)` | gfortran, nag, xlf, f18 | ifort | nvfortran | | 738| `CALL ACOS(X)` | | | gfortran, nag, xlf, nvfortran, ifort, f18 | | 739 740 741The rationale for f18 behavior is that when referring to a procedure with an 742argument number or type that does not match the intrinsic specification, it seems safer to block 743the rather likely case where the user is using the intrinsic the wrong way. 744In case the user wanted to refer to an external function, he can add an explicit EXTERNAL 745statement with no other consequences on the program. 746However, it seems rather unlikely that a user would confuse an intrinsic subroutine for a 747function and vice versa. Given no compiler is issuing an error here, changing the behavior might 748affect existing programs that omit the EXTERNAL attribute in such case. 749 750Also note that in general, the standard gives the compiler the right to consider 751any procedure that is not explicitly external as a non standard intrinsic (section 4.2 point 4). 752So it is highly advised for the programmer to use EXTERNAL statements to prevent any ambiguity. 753 754## Intrinsic Procedure Support in f18 755This section gives an overview of the support inside f18 libraries for the 756intrinsic procedures listed above. 757It may be outdated, refer to f18 code base for the actual support status. 758 759### Semantic Analysis 760F18 semantic expression analysis phase detects intrinsic procedure references, 761validates the argument types and deduces the return types. 762This phase currently supports all the intrinsic procedures listed above but the ones in the table below. 763 764| Intrinsic Category | Intrinsic Procedures Lacking Support | 765| --- | --- | 766| Coarray intrinsic functions | COSHAPE | 767| Object characteristic inquiry functions | ALLOCATED, ASSOCIATED, EXTENDS_TYPE_OF, IS_CONTIGUOUS, PRESENT, RANK, SAME_TYPE, STORAGE_SIZE | 768| Type inquiry intrinsic functions | BIT_SIZE, DIGITS, EPSILON, HUGE, KIND, MAXEXPONENT, MINEXPONENT, NEW_LINE, PRECISION, RADIX, RANGE, TINY| 769| Non-standard intrinsic functions | AND, OR, XOR, SHIFT, ZEXT, IZEXT, COSD, SIND, TAND, ACOSD, ASIND, ATAND, ATAN2D, COMPL, EQV, NEQV, INT8, JINT, JNINT, KNINT, QCMPLX, DREAL, DFLOAT, QEXT, QFLOAT, QREAL, DNUM, NUM, JNUM, KNUM, QNUM, RNUM, RAN, RANF, ILEN, SIZEOF, MCLOCK, SECNDS, COTAN, IBCHNG, ISHA, ISHC, ISHL, IXOR, IARG, IARGC, NARGS, GETPID, NUMARG, BADDRESS, IADDR, CACHESIZE, EOF, FP_CLASS, INT_PTR_KIND, ISNAN, MALLOC, FREE, GETUID, GETGID | 770| Intrinsic subroutines |MVBITS (elemental), CHDIR, CPU_TIME, DATE_AND_TIME, EVENT_QUERY, EXECUTE_COMMAND_LINE, GET_COMMAND, GET_COMMAND_ARGUMENT, GET_ENVIRONMENT_VARIABLE, MOVE_ALLOC, RANDOM_INIT, RANDOM_NUMBER, RANDOM_SEED, SIGNAL, SLEEP, SYSTEM, SYSTEM_CLOCK | 771| Atomic intrinsic subroutines | ATOMIC_ADD | 772| Collective intrinsic subroutines | CO_REDUCE | 773| Library subroutines | BACKTRACE, FDATE, GETLOG, GETENV | 774 775 776### Intrinsic Function Folding 777Fortran Constant Expressions can contain references to a certain number of 778intrinsic functions (see Fortran 2018 standard section 10.1.12 for more details). 779Constant Expressions may be used to define kind arguments. Therefore, the semantic 780expression analysis phase must be able to fold references to intrinsic functions 781listed in section 10.1.12. 782 783F18 intrinsic function folding is either performed by implementations directly 784operating on f18 scalar types or by using host runtime functions and 785host hardware types. F18 supports folding elemental intrinsic functions over 786arrays when an implementation is provided for the scalars (regardless of whether 787it is using host hardware types or not). 788The status of intrinsic function folding support is given in the sub-sections below. 789 790#### Intrinsic Functions with Host Independent Folding Support 791Implementations using f18 scalar types enables folding intrinsic functions 792on any host and with any possible type kind supported by f18. The intrinsic functions 793listed below are folded using host independent implementations. 794 795| Return Type | Intrinsic Functions with Host Independent Folding Support| 796| --- | --- | 797| INTEGER| ABS(INTEGER(k)), DIM(INTEGER(k), INTEGER(k)), DSHIFTL, DSHIFTR, IAND, IBCLR, IBSET, IEOR, INT, IOR, ISHFT, KIND, LEN, LEADZ, MASKL, MASKR, MERGE_BITS, POPCNT, POPPAR, SHIFTA, SHIFTL, SHIFTR, TRAILZ | 798| REAL | ABS(REAL(k)), ABS(COMPLEX(k)), AIMAG, AINT, DPROD, REAL | 799| COMPLEX | CMPLX, CONJG | 800| LOGICAL | BGE, BGT, BLE, BLT | 801 802#### Intrinsic Functions with Host Dependent Folding Support 803Implementations using the host runtime may not be available for all supported 804f18 types depending on the host hardware types and the libraries available on the host. 805The actual support on a host depends on what the host hardware types are. 806The list below gives the functions that are folded using host runtime and the related C/C++ types. 807F18 automatically detects if these types match an f18 scalar type. If so, 808folding of the intrinsic functions will be possible for the related f18 scalar type, 809otherwise an error message will be produced by f18 when attempting to fold related intrinsic functions. 810 811| C/C++ Host Type | Intrinsic Functions with Host Standard C++ Library Based Folding Support | 812| --- | --- | 813| float, double and long double | ACOS, ACOSH, ASINH, ATAN, ATAN2, ATANH, COS, COSH, ERF, ERFC, EXP, GAMMA, HYPOT, LOG, LOG10, LOG_GAMMA, MOD, SIN, SQRT, SINH, SQRT, TAN, TANH | 814| std::complex for float, double and long double| ACOS, ACOSH, ASIN, ASINH, ATAN, ATANH, COS, COSH, EXP, LOG, SIN, SINH, SQRT, TAN, TANH | 815 816On top of the default usage of C++ standard library functions for folding described 817in the table above, it is possible to compile f18 evaluate library with 818[libpgmath](https://github.com/flang-compiler/flang/tree/master/runtime/libpgmath) 819so that it can be used for folding. To do so, one must have a compiled version 820of the libpgmath library available on the host and add 821`-DLIBPGMATH_DIR=<path to the compiled shared libpgmath library>` to the f18 cmake command. 822 823Libpgmath comes with real and complex functions that replace C++ standard library 824float and double functions to fold all the intrinsic functions listed in the table above. 825It has no long double versions. If the host long double matches an f18 scalar type, 826C++ standard library functions will still be used for folding expressions with this scalar type. 827Libpgmath adds the possibility to fold the following functions for f18 real scalar 828types related to host float and double types. 829 830| C/C++ Host Type | Additional Intrinsic Function Folding Support with Libpgmath (Optional) | 831| --- | --- | 832|float and double| BESSEL_J0, BESSEL_J1, BESSEL_JN (elemental only), BESSEL_Y0, BESSEL_Y1, BESSEL_Yn (elemental only), ERFC_SCALED | 833 834Libpgmath comes in three variants (precise, relaxed and fast). So far, only the 835precise version is used for intrinsic function folding in f18. It guarantees the greatest numerical precision. 836 837### Intrinsic Functions with Missing Folding Support 838The following intrinsic functions are allowed in constant expressions but f18 839is not yet able to fold them. Note that there might be constraints on the arguments 840so that these intrinsics can be used in constant expressions (see section 10.1.12 of Fortran 2018 standard). 841 842ALL, ACHAR, ADJUSTL, ADJUSTR, ANINT, ANY, BESSEL_JN (transformational only), 843BESSEL_YN (transformational only), BTEST, CEILING, CHAR, COUNT, CSHIFT, DOT_PRODUCT, 844DIM (REAL only), DOT_PRODUCT, EOSHIFT, FINDLOC, FLOOR, FRACTION, HUGE, IACHAR, IALL, 845IANY, IPARITY, IBITS, ICHAR, IMAGE_STATUS, INDEX, ISHFTC, IS_IOSTAT_END, 846IS_IOSTAT_EOR, LBOUND, LEN_TRIM, LGE, LGT, LLE, LLT, LOGICAL, MATMUL, MAX, MAXLOC, 847MAXVAL, MERGE, MIN, MINLOC, MINVAL, MOD (INTEGER only), MODULO, NEAREST, NINT, 848NORM2, NOT, OUT_OF_RANGE, PACK, PARITY, PRODUCT, REPEAT, REDUCE, RESHAPE, 849RRSPACING, SCAN, SCALE, SELECTED_CHAR_KIND, SELECTED_INT_KIND, SELECTED_REAL_KIND, 850SET_EXPONENT, SHAPE, SIGN, SIZE, SPACING, SPREAD, SUM, TINY, TRANSFER, TRANSPOSE, 851TRIM, UBOUND, UNPACK, VERIFY. 852 853Coarray, non standard, IEEE and ISO_C_BINDINGS intrinsic functions that can be 854used in constant expressions have currently no folding support at all. 855 856### Standard Intrinsics: EXECUTE_COMMAND_LINE 857 858#### Usage and Info 859 860- **Standard:** Fortran 2008 and later, specified in subclause 16.9.73 861- **Class:** Subroutine 862- **Syntax:** `CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT, CMDMSG ])` 863- **Arguments:** 864 865| Argument | Description | 866|------------|-----------------------------------------------------------------------| 867| `COMMAND` | Shall be a default CHARACTER scalar. | 868| `WAIT` | (Optional) Shall be a default LOGICAL scalar. | 869| `EXITSTAT` | (Optional) Shall be an INTEGER with kind greater than or equal to 4. | 870| `CMDSTAT` | (Optional) Shall be an INTEGER with kind greater than or equal to 2. | 871| `CMDMSG` | (Optional) Shall be a CHARACTER scalar of the default kind. | 872 873#### Implementation Specifics 874 875##### `COMMAND`: 876 877- Must be preset. 878 879##### `WAIT`: 880 881- If set to `false`, the command is executed asynchronously. 882- If not preset or set to `true`, it is executed synchronously. 883- Synchronous execution is achieved by passing the command into `std::system` on all systems. 884- Asynchronous execution is achieved by calling `fork()` on POSIX-compatible systems or `CreateProcess()` on Windows. 885 886##### `EXITSTAT`: 887 888- Synchronous execution: 889 - Inferred by the return value of `std::system(cmd)`. 890 - On POSIX-compatible systems: return value is first passed into `WEXITSTATUS(status)`, then assigned to `EXITSTAT`. 891 - On Windows, the value is directly assigned as the return value of `std::system()`. 892- Asynchronous execution: 893 - Value is not modified. 894 895##### `CMDSTAT`: 896 897- Synchronous execution: 898 - -2: `ASYNC_NO_SUPPORT_ERR` - No error condition occurs, but `WAIT` is present with the value `false`, and the processor does not support asynchronous execution. 899 - -1: `NO_SUPPORT_ERR` - The processor does not support command line execution. (system returns -1 with errno `ENOENT`) 900 - 0: `CMD_EXECUTED` - Command executed with no error. 901 - \+ (positive value): An error condition occurs. 902 - 1: `FORK_ERR` - Fork Error (occurs only on POSIX-compatible systems). 903 - 2: `EXECL_ERR` - Execution Error (system returns -1 with other errno). 904 - 3: `COMMAND_EXECUTION_ERR` - Invalid Command Error (exit code 1). 905 - 4: `COMMAND_CANNOT_EXECUTE_ERR` - Command Cannot Execute Error (Linux exit code 126). 906 - 5: `COMMAND_NOT_FOUND_ERR` - Command Not Found Error (Linux exit code 127). 907 - 6: `INVALID_CL_ERR` - Invalid Command Line Error (covers all other non-zero exit codes). 908 - 7: `SIGNAL_ERR` - Signal error (either stopped or killed by signal, occurs only on POSIX-compatible systems). 909- Asynchronous execution: 910 - 0 will always be assigned. 911 912##### `CMDMSG`: 913 914- Synchronous execution: 915 - If an error condition occurs, it is assigned an explanatory message; otherwise, it remains unchanged. 916 - If a condition occurs that would assign a nonzero value to `CMDSTAT` but the `CMDSTAT` variable is not present, error termination is initiated (applies to both POSIX-compatible systems and Windows). 917- Asynchronous execution: 918 - The value is unchanged. 919 - If a condition occurs that would assign a nonzero value to `CMDSTAT` but the `CMDSTAT` variable is not present, error termination is initiated. 920 - On POSIX-compatible systems, the child process (async process) will be terminated with no effect on the parent process (continues). 921 - On Windows, error termination is not initiated. 922 923### Non-Standard Intrinsics: ETIME 924 925#### Description 926`ETIME(VALUES, TIME)` returns the number of seconds of runtime since the start of the process’s execution in *TIME*. *VALUES* returns the user and system components of this time in `VALUES(1)` and `VALUES(2)` respectively. *TIME* is equal to `VALUES(1) + VALUES(2)`. 927 928On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program. 929 930This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit. 931 932*VALUES* and *TIME* are `INTENT(OUT)` and provide the following: 933 934 935| | | 936|---------------|-----------------------------------| 937| `VALUES(1)` | User time in seconds. | 938| `VALUES(2)` | System time in seconds. | 939| `TIME` | Run time since start in seconds. | 940 941#### Usage and Info 942 943- **Standard:** GNU extension 944- **Class:** Subroutine, function 945- **Syntax:** `CALL ETIME(VALUES, TIME)` 946- **Arguments:** 947- **Return value** Elapsed time in seconds since the start of program execution. 948 949| Argument | Description | 950|------------|-----------------------------------------------------------------------| 951| `VALUES` | The type shall be REAL(4), DIMENSION(2). | 952| `TIME` | The type shall be REAL(4). | 953 954#### Example 955Here is an example usage from [Gfortran ETIME](https://gcc.gnu.org/onlinedocs/gfortran/ETIME.html) 956```Fortran 957program test_etime 958 integer(8) :: i, j 959 real, dimension(2) :: tarray 960 real :: result 961 call ETIME(tarray, result) 962 print *, result 963 print *, tarray(1) 964 print *, tarray(2) 965 do i=1,100000000 ! Just a delay 966 j = i * i - i 967 end do 968 call ETIME(tarray, result) 969 print *, result 970 print *, tarray(1) 971 print *, tarray(2) 972end program test_etime 973``` 974 975### Non-Standard Intrinsics: GETCWD 976 977#### Description 978`GETCWD(C, STATUS)` returns current working directory. 979 980This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit. 981 982*C* and *STATUS* are `INTENT(OUT)` and provide the following: 983 984| | | 985|------------|---------------------------------------------------------------------------------------------------| 986| `C` | Current work directory. The type shall be `CHARACTER` and of default kind. | 987| `STATUS` | (Optional) Status flag. Returns 0 on success, a system specific and nonzero error code otherwise. The type shall be `INTEGER` and of a kind greater or equal to 4. | 988 989#### Usage and Info 990 991- **Standard:** GNU extension 992- **Class:** Subroutine, function 993- **Syntax:** `CALL GETCWD(C, STATUS)`, `STATUS = GETCWD(C)` 994 995#### Example 996```Fortran 997PROGRAM example_getcwd 998 CHARACTER(len=255) :: cwd 999 INTEGER :: status 1000 CALL getcwd(cwd, status) 1001 PRINT *, cwd 1002 PRINT *, status 1003END PROGRAM 1004``` 1005 1006### Non-standard Intrinsics: RENAME 1007`RENAME(OLD, NEW[, STATUS])` renames/moves a file on the filesystem. 1008 1009This intrinsic is provided in both subroutine and function form; however, only one form can be used in any given program unit. 1010 1011#### Usage and Info 1012 1013- **Standard:** GNU extension 1014- **Class:** Subroutine, function 1015- **Syntax:** `CALL RENAME(SRC, DST[, STATUS])` 1016- **Arguments:** 1017- **Return value** status code (0: success, non-zero for errors) 1018 1019| Argument | Description | 1020|----------|-----------------------------------| 1021| `SRC` | Source path | 1022| `DST` | Destination path | 1023| `STATUS` | Status code (for subroutine form) | 1024 1025The status code returned by both the subroutine and function form corresponds to the value of `errno` if the invocation of `rename(2)` was not successful. 1026 1027#### Example 1028 1029Function form: 1030``` 1031program rename_func 1032 implicit none 1033 integer :: status 1034 status = rename('src', 'dst') 1035 print *, 'status:', status 1036 status = rename('dst', 'src') 1037 print *, 'status:', status 1038end program rename_func 1039``` 1040 1041Subroutine form: 1042``` 1043program rename_proc 1044 implicit none 1045 integer :: status 1046 call rename('src', 'dst', status) 1047 print *, 'status:', status 1048 call rename('dst', 'src') 1049end program rename_proc 1050``` 1051 1052### Non-standard Intrinsics: SECOND 1053This intrinsic is an alias for `CPU_TIME`: supporting both a subroutine and a 1054function form. 1055 1056### Non-standard Intrinsics: LNBLNK 1057This intrinsic is an alias for `LEN_TRIM`, without the optional KIND argument. 1058 1059#### Usage and Info 1060 1061- **Standard:** GNU extension 1062- **Class:** Subroutine, function 1063- **Syntax:** `CALL SECOND(TIME)` or `TIME = SECOND()` 1064- **Arguments:** `TIME` - a REAL value into which the elapsed CPU time in 1065 seconds is written 1066- **RETURN value:** same as TIME argument 1067 1068### Non-Standard Intrinsics: CHDIR 1069 1070#### Description 1071`CHDIR(NAME[, STATUS])` Change current working directory to a specified path. 1072 1073This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit. 1074*STATUS* is `INTENT(OUT)` and provide the following: 1075 1076| | | 1077|------------|---------------------------------------------------------------------------------------------------| 1078| `NAME` | The type shall be `CHARACTER` of default kind and shall specify a valid path within the file system. | 1079| `STATUS` | (Optional) Status flag. Returns 0 on success, a system specific and nonzero error code otherwise. The type shall be `INTEGER` and of the default kind. | 1080 1081#### Usage and Info 1082 1083- **Standard:** GNU extension 1084- **Class:** Subroutine, function 1085- **Syntax:** `CALL CHDIR(NAME[, STATUS])` and `STATUS = CHDIR(NAME)` 1086 1087#### Example 1088```Fortran 1089program chdir_func 1090 character(len=) :: path 1091 integer :: status 1092 1093 call chdir("/tmp") 1094 status = chdir("..") 1095 print *, "status: ", status 1096end program chdir_func 1097``` 1098 1099### Non-Standard Intrinsics: IERRNO 1100 1101#### Description 1102`IERRNO()` returns the last system error number, as given by the C `errno` variable. 1103 1104#### Usage and Info 1105 1106- **Standard:** GNU extension 1107- **Class:** function 1108- **Syntax:** `RESULT = IERRNO()` 1109