mingw-w64-crt/math/softmath/e_fmod.c

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
 * __ieee754_fmod(x,y)
 * Return x mod y in exact arithmetic
 * Method: shift and subtract
 */

#include "bsd_private.h"

double bsd__ieee754_fmod(double x, double y)
{
    int32_t n,hx,hy,hz,ix,iy,sx,i;
    u_int32_t lx,ly,lz;

    EXTRACT_WORDS(hx,lx,x);
    EXTRACT_WORDS(hy,ly,y);
    sx = hx&0x80000000;        /* sign of x */
    hx ^=sx;                   /* |x| */
    hy &= 0x7fffffff;          /* |y| */

    /* purge off exception values */
    if((hy|ly)==0||(hx>=0x7ff00000)||      /* y=0,or x not finite */
      ((hy|((ly|-ly)>>31))>0x7ff00000))    /* or y is NaN */
        return (x*y)/(x*y);
    if(hx<=hy) {
        if((hx<hy)||(lx<ly)) return x;     /* |x|<|y| return x */
        if(lx==ly)
        return Zero[(u_int32_t)sx>>31];    /* |x|=|y| return x*0*/
    }

    /* determine ix = ilogb(x) */
    if(hx<0x00100000) {    /* subnormal x */
        if(hx==0) {
            for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
        } else {
            for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
        }
    } else ix = (hx>>20)-1023;

    /* determine iy = ilogb(y) */
    if(hy<0x00100000) {    /* subnormal y */
        if(hy==0) {
            for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
        } else {
            for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
        }
    } else iy = (hy>>20)-1023;

    /* set up {hx,lx}, {hy,ly} and align y to x */
    if(ix >= -1022)
        hx = 0x00100000|(0x000fffff&hx);
    else {        /* subnormal x, shift x to normal */
        n = -1022-ix;
        if(n<=31) {
            hx = (hx<<n)|(lx>>(32-n));
            lx <<= n;
        } else {
            hx = lx<<(n-32);
            lx = 0;
        }
    }
    if(iy >= -1022)
        hy = 0x00100000|(0x000fffff&hy);
    else {        /* subnormal y, shift y to normal */
        n = -1022-iy;
        if(n<=31) {
            hy = (hy<<n)|(ly>>(32-n));
            ly <<= n;
        } else {
            hy = ly<<(n-32);
            ly = 0;
        }
    }

    /* fix point fmod */
    n = ix - iy;
    while(n--) {
        hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
        if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
        else {
            if((hz|lz)==0)    /* return sign(x)*0 */
                return Zero[(u_int32_t)sx>>31];
            hx = hz+hz+(lz>>31); lx = lz+lz;
        }
    }
    hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
    if(hz>=0) {hx=hz;lx=lz;}

    /* convert back to floating value and restore the sign */
    if((hx|lx)==0)                /* return sign(x)*0 */
        return Zero[(u_int32_t)sx>>31];
    while(hx<0x00100000) {        /* normalize x */
        hx = hx+hx+(lx>>31); lx = lx+lx;
        iy -= 1;
    }
    if(iy>= -1022) {     /* normalize output */
        hx = ((hx-0x00100000)|((iy+1023)<<20));
        INSERT_WORDS(x,hx|sx,lx);
    } else {             /* subnormal output */
        n = -1022 - iy;
        if(n<=20) {
            lx = (lx>>n)|((u_int32_t)hx<<(32-n));
            hx >>= n;
        } else if (n<=31) {
            lx = (hx<<(32-n))|(lx>>n); hx = sx;
        } else {
            lx = hx>>(n-32); hx = sx;
        }
        INSERT_WORDS(x,hx|sx,lx);
        x *= one;        /* create necessary signal */
    }
    return x;            /* exact output */
}