1 /* @(#)e_fmod.c 1.3 95/01/18 */ 2 /*- 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunSoft, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 #include <sys/cdefs.h> 14 15 #include "namespace.h" 16 17 #include "math.h" 18 #include "math_private.h" 19 20 #ifdef __weak_alias 21 __weak_alias(remquof, _remquof) 22 #endif 23 24 static const float Zero[] = {0.0, -0.0,}; 25 26 /* 27 * Return the IEEE remainder and set *quo to the last n bits of the 28 * quotient, rounded to the nearest integer. We choose n=31 because 29 * we wind up computing all the integer bits of the quotient anyway as 30 * a side-effect of computing the remainder by the shift and subtract 31 * method. In practice, this is far more bits than are needed to use 32 * remquo in reduction algorithms. 33 */ 34 float 35 remquof(float x, float y, int *quo) 36 { 37 int32_t n,hx,hy,hz,ix,iy,sx,i; 38 u_int32_t q,sxy; 39 40 GET_FLOAT_WORD(hx,x); 41 GET_FLOAT_WORD(hy,y); 42 sxy = (hx ^ hy) & 0x80000000; 43 sx = hx&0x80000000; /* sign of x */ 44 hx ^=sx; /* |x| */ 45 hy &= 0x7fffffff; /* |y| */ 46 47 /* purge off exception values */ 48 if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */ 49 return (x*y)/(x*y); 50 if(hx<hy) { 51 q = 0; 52 goto fixup; /* |x|<|y| return x or x-y */ 53 } else if(hx==hy) { 54 *quo = 1; 55 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ 56 } 57 58 /* determine ix = ilogb(x) */ 59 if(hx<0x00800000) { /* subnormal x */ 60 for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1; 61 } else ix = (hx>>23)-127; 62 63 /* determine iy = ilogb(y) */ 64 if(hy<0x00800000) { /* subnormal y */ 65 for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1; 66 } else iy = (hy>>23)-127; 67 68 /* set up {hx,lx}, {hy,ly} and align y to x */ 69 if(ix >= -126) 70 hx = 0x00800000|(0x007fffff&hx); 71 else { /* subnormal x, shift x to normal */ 72 n = -126-ix; 73 hx <<= n; 74 } 75 if(iy >= -126) 76 hy = 0x00800000|(0x007fffff&hy); 77 else { /* subnormal y, shift y to normal */ 78 n = -126-iy; 79 hy <<= n; 80 } 81 82 /* fix point fmod */ 83 n = ix - iy; 84 q = 0; 85 while(n--) { 86 hz=hx-hy; 87 if(hz<0) hx = hx << 1; 88 else {hx = hz << 1; q++;} 89 q <<= 1; 90 } 91 hz=hx-hy; 92 if(hz>=0) {hx=hz;q++;} 93 94 /* convert back to floating value and restore the sign */ 95 if(hx==0) { /* return sign(x)*0 */ 96 *quo = (sxy ? -q : q); 97 return Zero[(u_int32_t)sx>>31]; 98 } 99 while(hx<0x00800000) { /* normalize x */ 100 hx <<= 1; 101 iy -= 1; 102 } 103 if(iy>= -126) { /* normalize output */ 104 hx = ((hx-0x00800000)|((iy+127)<<23)); 105 } else { /* subnormal output */ 106 n = -126 - iy; 107 hx >>= n; 108 } 109 fixup: 110 SET_FLOAT_WORD(x,hx); 111 y = fabsf(y); 112 if (y < 0x1p-125f) { 113 if (x+x>y || (x+x==y && (q & 1))) { 114 q++; 115 x-=y; 116 } 117 } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) { 118 q++; 119 x-=y; 120 } 121 GET_FLOAT_WORD(hx,x); 122 SET_FLOAT_WORD(x,hx^sx); 123 q &= 0x7fffffff; 124 *quo = (sxy ? -q : q); 125 return x; 126 } 127