1 /* $OpenBSD: ldexp.c,v 1.1 2009/04/19 16:42:06 martynas Exp $ */ 2 /* @(#)s_scalbn.c 5.1 93/09/24 */ 3 /* @(#)fdlibm.h 5.1 93/09/24 */ 4 /* 5 * ==================================================== 6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 7 * 8 * Developed at SunPro, a Sun Microsystems, Inc. business. 9 * Permission to use, copy, modify, and distribute this 10 * software is freely granted, provided that this notice 11 * is preserved. 12 * ==================================================== 13 */ 14 15 #if 0 16 __FBSDID("$FreeBSD: src/lib/libc/gen/ldexp.c,v 1.1 2005/01/22 06:03:40 das Exp $"); 17 #endif 18 19 #include <sys/types.h> 20 #include <sys/cdefs.h> 21 #include <machine/endian.h> 22 #include <float.h> 23 #include <math.h> 24 25 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */ 26 27 #if BYTE_ORDER == BIG_ENDIAN 28 29 typedef union 30 { 31 double value; 32 struct 33 { 34 u_int32_t msw; 35 u_int32_t lsw; 36 } parts; 37 } ieee_double_shape_type; 38 39 #endif 40 41 #if BYTE_ORDER == LITTLE_ENDIAN 42 43 typedef union 44 { 45 double value; 46 struct 47 { 48 u_int32_t lsw; 49 u_int32_t msw; 50 } parts; 51 } ieee_double_shape_type; 52 53 #endif 54 55 /* Get two 32 bit ints from a double. */ 56 57 #define EXTRACT_WORDS(ix0,ix1,d) \ 58 do { \ 59 ieee_double_shape_type ew_u; \ 60 ew_u.value = (d); \ 61 (ix0) = ew_u.parts.msw; \ 62 (ix1) = ew_u.parts.lsw; \ 63 } while (0) 64 65 /* Get the more significant 32 bit int from a double. */ 66 67 #define GET_HIGH_WORD(i,d) \ 68 do { \ 69 ieee_double_shape_type gh_u; \ 70 gh_u.value = (d); \ 71 (i) = gh_u.parts.msw; \ 72 } while (0) 73 74 /* Set the more significant 32 bits of a double from an int. */ 75 76 #define SET_HIGH_WORD(d,v) \ 77 do { \ 78 ieee_double_shape_type sh_u; \ 79 sh_u.value = (d); \ 80 sh_u.parts.msw = (v); \ 81 (d) = sh_u.value; \ 82 } while (0) 83 84 85 static const double 86 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 87 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 88 huge = 1.0e+300, 89 tiny = 1.0e-300; 90 91 static double 92 _copysign(double x, double y) 93 { 94 u_int32_t hx,hy; 95 GET_HIGH_WORD(hx,x); 96 GET_HIGH_WORD(hy,y); 97 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000)); 98 return x; 99 } 100 101 double 102 ldexp(double x, int n) 103 { 104 int32_t k,hx,lx; 105 EXTRACT_WORDS(hx,lx,x); 106 k = (hx&0x7ff00000)>>20; /* extract exponent */ 107 if (k==0) { /* 0 or subnormal x */ 108 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 109 x *= two54; 110 GET_HIGH_WORD(hx,x); 111 k = ((hx&0x7ff00000)>>20) - 54; 112 if (n< -50000) return tiny*x; /*underflow*/ 113 } 114 if (k==0x7ff) return x+x; /* NaN or Inf */ 115 k = k+n; 116 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */ 117 if (k > 0) /* normal result */ 118 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 119 if (k <= -54) { 120 if (n > 50000) /* in case integer overflow in n+k */ 121 return huge*_copysign(huge,x); /*overflow*/ 122 else return tiny*_copysign(tiny,x); /*underflow*/ 123 } 124 k += 54; /* subnormal result */ 125 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 126 return x*twom54; 127 } 128 129 #if LDBL_MANT_DIG == 53 130 #ifdef __weak_alias 131 __weak_alias(ldexpl, ldexp); 132 #endif /* __weak_alias */ 133 #endif /* LDBL_MANT_DIG == 53 */ 134