compiler/stdc/math/s_remquof.c

   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 __FBSDID("$FreeBSD: src/lib/msun/src/s_remquof.c,v 1.1 2005/03/25 04:40:44 das Exp $");
  14
  15 #include "math.h"
  16 #include "math_private.h"
  17
  18 static const float Zero[] = {0.0, -0.0,};
  19
  20 /*
  21  * Return the IEEE remainder and set *quo to the last n bits of the
  22  * quotient, rounded to the nearest integer.  We choose n=31 because
  23  * we wind up computing all the integer bits of the quotient anyway as
  24  * a side-effect of computing the remainder by the shift and subtract
  25  * method.  In practice, this is far more bits than are needed to use
  26  * remquo in reduction algorithms.
  27  */
  28 float
  29 remquof(float x, float y, int *quo)
  30 {
  31         int32_t n,hx,hy,hz,ix,iy,sx,i;
  32         uint32_t q,sxy;
  33
  34         GET_FLOAT_WORD(hx,x);
  35         GET_FLOAT_WORD(hy,y);
  36         sxy = (hx ^ hy) & 0x80000000;
  37         sx = hx&0x80000000;             /* sign of x */
  38         hx ^=sx;                /* |x| */
  39         hy &= 0x7fffffff;       /* |y| */
  40
  41     /* purge off exception values */
  42         if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
  43             return (x*y)/(x*y);
  44         if(hx<hy) {
  45             q = 0;
  46             goto fixup; /* |x|<|y| return x or x-y */
  47         } else if(hx==hy) {
  48             *quo = 1;
  49             return Zero[(uint32_t)sx>>31];      /* |x|=|y| return x*0*/
  50         }
  51
  52     /* determine ix = ilogb(x) */
  53         if(hx<0x00800000) {     /* subnormal x */
  54             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  55         } else ix = (hx>>23)-127;
  56
  57     /* determine iy = ilogb(y) */
  58         if(hy<0x00800000) {     /* subnormal y */
  59             for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
  60         } else iy = (hy>>23)-127;
  61
  62     /* set up {hx,lx}, {hy,ly} and align y to x */
  63         if(ix >= -126)
  64             hx = 0x00800000|(0x007fffff&hx);
  65         else {          /* subnormal x, shift x to normal */
  66             n = -126-ix;
  67             hx <<= n;
  68         }
  69         if(iy >= -126)
  70             hy = 0x00800000|(0x007fffff&hy);
  71         else {          /* subnormal y, shift y to normal */
  72             n = -126-iy;
  73             hy <<= n;
  74         }
  75
  76     /* fix point fmod */
  77         n = ix - iy;
  78         q = 0;
  79         while(n--) {
  80             hz=hx-hy;
  81             if(hz<0) hx = hx << 1;
  82             else {hx = hz << 1; q++;}
  83             q <<= 1;
  84         }
  85         hz=hx-hy;
  86         if(hz>=0) {hx=hz;q++;}
  87
  88     /* convert back to floating value and restore the sign */
  89         if(hx==0) {                             /* return sign(x)*0 */
  90             *quo = (sxy ? -q : q);
  91             return Zero[(uint32_t)sx>>31];
  92         }
  93         while(hx<0x00800000) {          /* normalize x */
  94             hx <<= 1;
  95             iy -= 1;
  96         }
  97         if(iy>= -126) {         /* normalize output */
  98             hx = ((hx-0x00800000)|((iy+127)<<23));
  99         } else {                /* subnormal output */
 100             n = -126 - iy;
 101             hx >>= n;
 102         }
 103 fixup:
 104         SET_FLOAT_WORD(x,hx);
 105         y = fabsf(y);
 106         if (y < 0x1p-125f) {
 107             if (x+x>y || (x+x==y && (q & 1))) {
 108                 q++;
 109                 x-=y;
 110             }
 111         } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
 112             q++;
 113             x-=y;
 114         }
 115         GET_FLOAT_WORD(hx,x);
 116         SET_FLOAT_WORD(x,hx^sx);
 117         q &= 0x7fffffff;
 118         *quo = (sxy ? -q : q);
 119         return x;
 120 }