1 /* @(#)s_scalbn.c 5.1 93/09/24 */ 2 /* @(#)fdlibm.h 5.1 93/09/24 */ 3 /* $FreeBSD: head/lib/libc/gen/ldexp.c 140607 2005-01-22 06:03:40Z das $ */ 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 #include <sys/types.h> 16 #include <machine/endian.h> 17 #include <math.h> 18 19 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */ 20 21 #if BYTE_ORDER == BIG_ENDIAN 22 23 typedef union 24 { 25 double value; 26 struct 27 { 28 u_int32_t msw; 29 u_int32_t lsw; 30 } parts; 31 } ieee_double_shape_type; 32 33 #endif 34 35 #if BYTE_ORDER == LITTLE_ENDIAN 36 37 typedef union 38 { 39 double value; 40 struct 41 { 42 u_int32_t lsw; 43 u_int32_t msw; 44 } parts; 45 } ieee_double_shape_type; 46 47 #endif 48 49 /* Get two 32 bit ints from a double. */ 50 51 #define EXTRACT_WORDS(ix0,ix1,d) \ 52 do { \ 53 ieee_double_shape_type ew_u; \ 54 ew_u.value = (d); \ 55 (ix0) = ew_u.parts.msw; \ 56 (ix1) = ew_u.parts.lsw; \ 57 } while (0) 58 59 /* Get the more significant 32 bit int from a double. */ 60 61 #define GET_HIGH_WORD(i,d) \ 62 do { \ 63 ieee_double_shape_type gh_u; \ 64 gh_u.value = (d); \ 65 (i) = gh_u.parts.msw; \ 66 } while (0) 67 68 /* Set the more significant 32 bits of a double from an int. */ 69 70 #define SET_HIGH_WORD(d,v) \ 71 do { \ 72 ieee_double_shape_type sh_u; \ 73 sh_u.value = (d); \ 74 sh_u.parts.msw = (v); \ 75 (d) = sh_u.value; \ 76 } while (0) 77 78 79 static const double 80 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 81 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 82 huge = 1.0e+300, 83 tiny = 1.0e-300; 84 85 static double 86 _copysign(double x, double y) 87 { 88 u_int32_t hx,hy; 89 GET_HIGH_WORD(hx,x); 90 GET_HIGH_WORD(hy,y); 91 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000)); 92 return x; 93 } 94 95 double 96 ldexp(double x, int n) 97 { 98 int32_t k,hx,lx; 99 EXTRACT_WORDS(hx,lx,x); 100 k = (hx&0x7ff00000)>>20; /* extract exponent */ 101 if (k==0) { /* 0 or subnormal x */ 102 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 103 x *= two54; 104 GET_HIGH_WORD(hx,x); 105 k = ((hx&0x7ff00000)>>20) - 54; 106 if (n< -50000) return tiny*x; /*underflow*/ 107 } 108 if (k==0x7ff) return x+x; /* NaN or Inf */ 109 k = k+n; 110 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */ 111 if (k > 0) /* normal result */ 112 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 113 if (k <= -54) { 114 if (n > 50000) /* in case integer overflow in n+k */ 115 return huge*_copysign(huge,x); /*overflow*/ 116 else return tiny*_copysign(tiny,x); /*underflow*/ 117 } 118 k += 54; /* subnormal result */ 119 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 120 return x*twom54; 121 } 122