e_fmod.c (3582B)
1 /* 2 * ==================================================== 3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 4 * 5 * Developed at SunPro, a Sun Microsystems, Inc. business. 6 * Permission to use, copy, modify, and distribute this 7 * software is freely granted, provided that this notice 8 * is preserved. 9 * ==================================================== 10 */ 11 12 /* 13 * __ieee754_fmod(x,y) 14 * Return x mod y in exact arithmetic 15 * Method: shift and subtract 16 */ 17 18 #include "math_libm.h" 19 #include "math_private.h" 20 21 static const double one = 1.0, Zero[] = {0.0, -0.0,}; 22 23 double attribute_hidden __ieee754_fmod(double x, double y) 24 { 25 int32_t n,hx,hy,hz,ix,iy,sx,i; 26 u_int32_t lx,ly,lz; 27 28 EXTRACT_WORDS(hx,lx,x); 29 EXTRACT_WORDS(hy,ly,y); 30 sx = hx&0x80000000; /* sign of x */ 31 hx ^=sx; /* |x| */ 32 hy &= 0x7fffffff; /* |y| */ 33 34 /* purge off exception values */ 35 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */ 36 ((hy|((ly|-(int32_t)ly)>>31))>0x7ff00000)) /* or y is NaN */ 37 return (x*y)/(x*y); 38 if(hx<=hy) { 39 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */ 40 if(lx==ly) 41 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ 42 } 43 44 /* determine ix = ilogb(x) */ 45 if(hx<0x00100000) { /* subnormal x */ 46 if(hx==0) { 47 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1; 48 } else { 49 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1; 50 } 51 } else ix = (hx>>20)-1023; 52 53 /* determine iy = ilogb(y) */ 54 if(hy<0x00100000) { /* subnormal y */ 55 if(hy==0) { 56 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1; 57 } else { 58 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1; 59 } 60 } else iy = (hy>>20)-1023; 61 62 /* set up {hx,lx}, {hy,ly} and align y to x */ 63 if(ix >= -1022) 64 hx = 0x00100000|(0x000fffff&hx); 65 else { /* subnormal x, shift x to normal */ 66 n = -1022-ix; 67 if(n<=31) { 68 hx = (hx<<n)|(lx>>(32-n)); 69 lx <<= n; 70 } else { 71 hx = lx<<(n-32); 72 lx = 0; 73 } 74 } 75 if(iy >= -1022) 76 hy = 0x00100000|(0x000fffff&hy); 77 else { /* subnormal y, shift y to normal */ 78 n = -1022-iy; 79 if(n<=31) { 80 hy = (hy<<n)|(ly>>(32-n)); 81 ly <<= n; 82 } else { 83 hy = ly<<(n-32); 84 ly = 0; 85 } 86 } 87 88 /* fix point fmod */ 89 n = ix - iy; 90 while(n--) { 91 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 92 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;} 93 else { 94 if((hz|lz)==0) /* return sign(x)*0 */ 95 return Zero[(u_int32_t)sx>>31]; 96 hx = hz+hz+(lz>>31); lx = lz+lz; 97 } 98 } 99 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 100 if(hz>=0) {hx=hz;lx=lz;} 101 102 /* convert back to floating value and restore the sign */ 103 if((hx|lx)==0) /* return sign(x)*0 */ 104 return Zero[(u_int32_t)sx>>31]; 105 while(hx<0x00100000) { /* normalize x */ 106 hx = hx+hx+(lx>>31); lx = lx+lx; 107 iy -= 1; 108 } 109 if(iy>= -1022) { /* normalize output */ 110 hx = ((hx-0x00100000)|((iy+1023)<<20)); 111 INSERT_WORDS(x,hx|sx,lx); 112 } else { /* subnormal output */ 113 n = -1022 - iy; 114 if(n<=20) { 115 lx = (lx>>n)|((u_int32_t)hx<<(32-n)); 116 hx >>= n; 117 } else if (n<=31) { 118 lx = (hx<<(32-n))|(lx>>n); hx = sx; 119 } else { 120 lx = hx>>(n-32); hx = sx; 121 } 122 INSERT_WORDS(x,hx|sx,lx); 123 x *= one; /* create necessary signal */ 124 } 125 return x; /* exact output */ 126 } 127 128 /* 129 * wrapper fmod(x,y) 130 */ 131 #ifndef _IEEE_LIBM 132 double fmod(double x, double y) 133 { 134 double z = __ieee754_fmod(x, y); 135 if (_LIB_VERSION == _IEEE_ || isnan(y) || isnan(x)) 136 return z; 137 if (y == 0.0) 138 return __kernel_standard(x, y, 27); /* fmod(x,0) */ 139 return z; 140 } 141 #else 142 strong_alias(__ieee754_fmod, fmod) 143 #endif 144 libm_hidden_def(fmod)