newlib/libm/mathfp/sf_fmod.c

   1 /* ef_fmod.c -- float version of e_fmod.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 /*
  17  * fmodf(x,y)
  18  * Return x mod y in exact arithmetic
  19  * Method: shift and subtract
  20  */
  21
  22 #include "fdlibm.h"
  23 #include "zmath.h"
  24
  25 static const float one = 1.0, Zero[] = {0.0, -0.0,};
  26
  27 float
  28 fmodf (float x,
  29         float y)
  30 {
  31         __int32_t n,hx,hy,hz,ix,iy,sx,i;
  32
  33         GET_FLOAT_WORD(hx,x);
  34         GET_FLOAT_WORD(hy,y);
  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)||            /* y=0,or x not finite */
  41            (hy>0x7f800000))                     /* or y is NaN */
  42             return (x*y)/(x*y);
  43         if(hx<hy) return x;                     /* |x|<|y| return x */
  44         if(hx==hy)
  45             return Zero[(__uint32_t)sx>>31];    /* |x|=|y| return x*0*/
  46
  47     /* determine ix = ilogb(x) */
  48         if(hx<0x00800000) {     /* subnormal x */
  49             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  50         } else ix = (hx>>23)-127;
  51
  52     /* determine iy = ilogb(y) */
  53         if(hy<0x00800000) {     /* subnormal y */
  54             for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
  55         } else iy = (hy>>23)-127;
  56
  57     /* set up {hx,lx}, {hy,ly} and align y to x */
  58         if(ix >= -126)
  59             hx = 0x00800000|(0x007fffff&hx);
  60         else {          /* subnormal x, shift x to normal */
  61             n = -126-ix;
  62             hx = hx<<n;
  63         }
  64         if(iy >= -126)
  65             hy = 0x00800000|(0x007fffff&hy);
  66         else {          /* subnormal y, shift y to normal */
  67             n = -126-iy;
  68             hy = hy<<n;
  69         }
  70
  71     /* fix point fmod */
  72         n = ix - iy;
  73         while(n--) {
  74             hz=hx-hy;
  75             if(hz<0){hx = hx+hx;}
  76             else {
  77                 if(hz==0)               /* return sign(x)*0 */
  78                     return Zero[(__uint32_t)sx>>31];
  79                 hx = hz+hz;
  80             }
  81         }
  82         hz=hx-hy;
  83         if(hz>=0) {hx=hz;}
  84
  85     /* convert back to floating value and restore the sign */
  86         if(hx==0)                       /* return sign(x)*0 */
  87             return Zero[(__uint32_t)sx>>31];
  88         while(hx<0x00800000) {          /* normalize x */
  89             hx = hx+hx;
  90             iy -= 1;
  91         }
  92         if(iy>= -126) {         /* normalize output */
  93             hx = ((hx-0x00800000)|((iy+127)<<23));
  94             SET_FLOAT_WORD(x,hx|sx);
  95         } else {                /* subnormal output */
  96             n = -126 - iy;
  97             hx >>= n;
  98             SET_FLOAT_WORD(x,hx|sx);
  99             x *= one;           /* create necessary signal */
 100         }
 101         return x;               /* exact output */
 102 }