1 /*===-- floatdidf.c - Implement __floatdidf -------------------------------=== 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is dual licensed under the MIT and the University of Illinois Open 6 * Source Licenses. See LICENSE.TXT for details. 7 * 8 *===----------------------------------------------------------------------=== 9 * 10 * This file implements __floatdidf for the compiler_rt library. 11 * 12 *===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 /* Returns: convert a to a double, rounding toward even. */ 18 19 /* Assumption: double is a IEEE 64 bit floating point type 20 * di_int is a 64 bit integral type 21 */ 22 23 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 24 ARM_EABI_FNALIAS(l2d,floatdidf)25 ARM_EABI_FNALIAS(l2d, floatdidf) 26 27 #ifndef __SOFT_FP__ 28 /* Support for systems that have hardware floating-point; we'll set the inexact flag 29 * as a side-effect of this computation. 30 */ 31 32 COMPILER_RT_ABI double 33 __floatdidf(di_int a) 34 { 35 static const double twop52 = 0x1.0p52; 36 static const double twop32 = 0x1.0p32; 37 38 union { int64_t x; double d; } low = { .d = twop52 }; 39 40 const double high = (int32_t)(a >> 32) * twop32; 41 low.x |= a & INT64_C(0x00000000ffffffff); 42 43 const double result = (high - twop52) + low.d; 44 return result; 45 } 46 47 #else 48 /* Support for systems that don't have hardware floating-point; there are no flags to 49 * set, and we don't want to code-gen to an unknown soft-float implementation. 50 */ 51 52 COMPILER_RT_ABI double 53 __floatdidf(di_int a) 54 { 55 if (a == 0) 56 return 0.0; 57 const unsigned N = sizeof(di_int) * CHAR_BIT; 58 const di_int s = a >> (N-1); 59 a = (a ^ s) - s; 60 int sd = N - __builtin_clzll(a); /* number of significant digits */ 61 int e = sd - 1; /* exponent */ 62 if (sd > DBL_MANT_DIG) 63 { 64 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 65 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 66 * 12345678901234567890123456 67 * 1 = msb 1 bit 68 * P = bit DBL_MANT_DIG-1 bits to the right of 1 69 * Q = bit DBL_MANT_DIG bits to the right of 1 70 * R = "or" of all bits to the right of Q 71 */ 72 switch (sd) 73 { 74 case DBL_MANT_DIG + 1: 75 a <<= 1; 76 break; 77 case DBL_MANT_DIG + 2: 78 break; 79 default: 80 a = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) | 81 ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 82 }; 83 /* finish: */ 84 a |= (a & 4) != 0; /* Or P into R */ 85 ++a; /* round - this step may add a significant bit */ 86 a >>= 2; /* dump Q and R */ 87 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 88 if (a & ((du_int)1 << DBL_MANT_DIG)) 89 { 90 a >>= 1; 91 ++e; 92 } 93 /* a is now rounded to DBL_MANT_DIG bits */ 94 } 95 else 96 { 97 a <<= (DBL_MANT_DIG - sd); 98 /* a is now rounded to DBL_MANT_DIG bits */ 99 } 100 double_bits fb; 101 fb.u.high = ((su_int)s & 0x80000000) | /* sign */ 102 ((e + 1023) << 20) | /* exponent */ 103 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 104 fb.u.low = (su_int)a; /* mantissa-low */ 105 return fb.f; 106 } 107 #endif 108