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e_fmodf.c revision 1.2 
      1 /* e_fmodf.c -- float version of e_fmod.c.
      2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 #ifndef lint
     17 static char rcsid[] = "$Id: e_fmodf.c,v 1.2 1994/08/18 23:05:23 jtc Exp $";
     18 #endif
     19 
     20 /*
     21  * __ieee754_fmodf(x,y)
     22  * Return x mod y in exact arithmetic
     23  * Method: shift and subtract
     24  */
     25 
     26 #include "math.h"
     27 #include "math_private.h"
     28 
     29 #ifdef __STDC__
     30 static const float one = 1.0, Zero[] = {0.0, -0.0,};
     31 #else
     32 static float one = 1.0, Zero[] = {0.0, -0.0,};
     33 #endif
     34 
     35 #ifdef __STDC__
     36 	float __ieee754_fmodf(float x, float y)
     37 #else
     38 	float __ieee754_fmodf(x,y)
     39 	float x,y ;
     40 #endif
     41 {
     42 	int32_t n,hx,hy,hz,ix,iy,sx,i;
     43 
     44 	GET_FLOAT_WORD(hx,x);
     45 	GET_FLOAT_WORD(hy,y);
     46 	sx = hx&0x80000000;		/* sign of x */
     47 	hx ^=sx;		/* |x| */
     48 	hy &= 0x7fffffff;	/* |y| */
     49 
     50     /* purge off exception values */
     51 	if(hy==0||(hx>=0x7f800000)||		/* y=0,or x not finite */
     52 	   (hy>0x7f800000))			/* or y is NaN */
     53 	    return (x*y)/(x*y);
     54 	if(hx<hy) return x;			/* |x|<|y| return x */
     55 	if(hx==hy)
     56 	    return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
     57 
     58     /* determine ix = ilogb(x) */
     59 	if(hx<0x00800000) {	/* subnormal x */
     60 	    for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
     61 	} else ix = (hx>>23)-127;
     62 
     63     /* determine iy = ilogb(y) */
     64 	if(hy<0x00800000) {	/* subnormal y */
     65 	    for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1;
     66 	} else iy = (hy>>23)-127;
     67 
     68     /* set up {hx,lx}, {hy,ly} and align y to x */
     69 	if(ix >= -126)
     70 	    hx = 0x00800000|(0x007fffff&hx);
     71 	else {		/* subnormal x, shift x to normal */
     72 	    n = -126-ix;
     73 	    hx = hx<<n;
     74 	}
     75 	if(iy >= -126)
     76 	    hy = 0x00800000|(0x007fffff&hy);
     77 	else {		/* subnormal y, shift y to normal */
     78 	    n = -126-iy;
     79 	    hy = hy<<n;
     80 	}
     81 
     82     /* fix point fmod */
     83 	n = ix - iy;
     84 	while(n--) {
     85 	    hz=hx-hy;
     86 	    if(hz<0){hx = hx+hx;}
     87 	    else {
     88 	    	if(hz==0) 		/* return sign(x)*0 */
     89 		    return Zero[(u_int32_t)sx>>31];
     90 	    	hx = hz+hz;
     91 	    }
     92 	}
     93 	hz=hx-hy;
     94 	if(hz>=0) {hx=hz;}
     95 
     96     /* convert back to floating value and restore the sign */
     97 	if(hx==0) 			/* return sign(x)*0 */
     98 	    return Zero[(u_int32_t)sx>>31];
     99 	while(hx<0x00800000) {		/* normalize x */
    100 	    hx = hx+hx;
    101 	    iy -= 1;
    102 	}
    103 	if(iy>= -126) {		/* normalize output */
    104 	    hx = ((hx-0x00800000)|((iy+127)<<23));
    105 	    SET_FLOAT_WORD(x,hx|sx);
    106 	} else {		/* subnormal output */
    107 	    n = -126 - iy;
    108 	    hx >>= n;
    109 	    SET_FLOAT_WORD(x,hx|sx);
    110 	    x *= one;		/* create necessary signal */
    111 	}
    112 	return x;		/* exact output */
    113 }
    114