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 25 typedef 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 39 typedef 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) \ 54 do { \ 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) \ 64 do { \ 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) \ 73 do { \ 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 81 static const double 82 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 83 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 84 huge = 1.0e+300, 85 tiny = 1.0e-300; 86 87 static 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 97 double 98 ldexp(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