source: vendor/FreeBSD-msun/5.x-2005-06-xx/src/e_fmodf.c

/* e_fmodf.c -- float version of e_fmod.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * 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.
 * ====================================================
 */

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmodf.c,v 1.6 2002/05/28 17:03:12 alfred Exp $";
#endif

/*
 * __ieee754_fmodf(x,y)
 * Return x mod y in exact arithmetic
 * Method: shift and subtract
 */

#include "math.h"
#include "math_private.h"

static const float one = 1.0, Zero[] = {0.0, -0.0,};

float
__ieee754_fmodf(float x, float y)
{
        int32_t n,hx,hy,hz,ix,iy,sx,i;

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

    /* purge off exception values */
        if(hy==0||(hx>=0x7f800000)||            /* y=0,or x not finite */
           (hy>0x7f800000))                     /* or y is NaN */
            return (x*y)/(x*y);
        if(hx<hy) return x;                     /* |x|<|y| return x */
        if(hx==hy)
            return Zero[(u_int32_t)sx>>31];     /* |x|=|y| return x*0*/

    /* determine ix = ilogb(x) */
        if(hx<0x00800000) {     /* subnormal x */
            for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
        } else ix = (hx>>23)-127;

    /* determine iy = ilogb(y) */
        if(hy<0x00800000) {     /* subnormal y */
            for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
        } else iy = (hy>>23)-127;

    /* set up {hx,lx}, {hy,ly} and align y to x */
        if(ix >= -126)
            hx = 0x00800000|(0x007fffff&hx);
        else {          /* subnormal x, shift x to normal */
            n = -126-ix;
            hx = hx<<n;
        }
        if(iy >= -126)
            hy = 0x00800000|(0x007fffff&hy);
        else {          /* subnormal y, shift y to normal */
            n = -126-iy;
            hy = hy<<n;
        }

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

    /* convert back to floating value and restore the sign */
        if(hx==0)                       /* return sign(x)*0 */
            return Zero[(u_int32_t)sx>>31];
        while(hx<0x00800000) {          /* normalize x */
            hx = hx+hx;
            iy -= 1;
        }
        if(iy>= -126) {         /* normalize output */
            hx = ((hx-0x00800000)|((iy+127)<<23));
            SET_FLOAT_WORD(x,hx|sx);
        } else {                /* subnormal output */
            n = -126 - iy;
            hx >>= n;
            SET_FLOAT_WORD(x,hx|sx);
            x *= one;           /* create necessary signal */
        }
        return x;               /* exact output */
}