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 16 #include <sys/types.h> 17 #include <endian.h> 18 #include <math.h> 19 20 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */ 21 22 #if BYTE_ORDER == BIG_ENDIAN 23 24 typedef union 25 { 26 double value; 27 struct 28 { 29 u_int32_t msw; 30 u_int32_t lsw; 31 } parts; 32 } ieee_double_shape_type; 33 34 #endif 35 36 #if BYTE_ORDER == LITTLE_ENDIAN 37 38 typedef union 39 { 40 double value; 41 struct 42 { 43 u_int32_t lsw; 44 u_int32_t msw; 45 } parts; 46 } ieee_double_shape_type; 47 48 #endif 49 50 /* Get two 32 bit ints from a double. */ 51 52 #define EXTRACT_WORDS(ix0,ix1,d) \ 53 do { \ 54 ieee_double_shape_type ew_u; \ 55 ew_u.value = (d); \ 56 (ix0) = ew_u.parts.msw; \ 57 (ix1) = ew_u.parts.lsw; \ 58 } while (0) 59 60 /* Get the more significant 32 bit int from a double. */ 61 62 #define GET_HIGH_WORD(i,d) \ 63 do { \ 64 ieee_double_shape_type gh_u; \ 65 gh_u.value = (d); \ 66 (i) = gh_u.parts.msw; \ 67 } while (0) 68 69 /* Set the more significant 32 bits of a double from an int. */ 70 71 #define SET_HIGH_WORD(d,v) \ 72 do { \ 73 ieee_double_shape_type sh_u; \ 74 sh_u.value = (d); \ 75 sh_u.parts.msw = (v); \ 76 (d) = sh_u.value; \ 77 } while (0) 78 79 80 static const double 81 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 82 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 83 huge = 1.0e+300, 84 tiny = 1.0e-300; 85 86 static double 87 _copysign(double x, double y) 88 { 89 u_int32_t hx,hy; 90 GET_HIGH_WORD(hx,x); 91 GET_HIGH_WORD(hy,y); 92 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000)); 93 return x; 94 } 95 96 double 97 ldexp(double x, int n) 98 { 99 int32_t k,hx,lx; 100 EXTRACT_WORDS(hx,lx,x); 101 k = (hx&0x7ff00000)>>20; /* extract exponent */ 102 if (k==0) { /* 0 or subnormal x */ 103 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 104 x *= two54; 105 GET_HIGH_WORD(hx,x); 106 k = ((hx&0x7ff00000)>>20) - 54; 107 if (n< -50000) return tiny*x; /*underflow*/ 108 } 109 if (k==0x7ff) return x+x; /* NaN or Inf */ 110 k = k+n; 111 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */ 112 if (k > 0) /* normal result */ 113 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 114 if (k <= -54) { 115 if (n > 50000) /* in case integer overflow in n+k */ 116 return huge*_copysign(huge,x); /*overflow*/ 117 else return tiny*_copysign(tiny,x); /*underflow*/ 118 } 119 k += 54; /* subnormal result */ 120 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 121 return x*twom54; 122 } 123