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