ef_fmod.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/* ef_fmod.c -- float version of e_fmod.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, [e-mail].
 */

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

#include "fdlibm.h"

#ifdef __STDC__
static const float one = 1.0, Zero[] = {0.0, -0.0,};
#else
static float one = 1.0, Zero[] = {0.0, -0.0,};
#endif

#ifdef __STDC__
	float __ieee754_fmodf(float x, float y)
#else
	float __ieee754_fmodf(x,y)
	float x,y ;
#endif
{
	__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[(__uint32_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[(__uint32_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[(__uint32_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 */
}