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