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      1 /* @(#)e_fmod.c 1.3 95/01/18 */
      2 /*-
      3  * ====================================================
      4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      5  *
      6  * Developed at SunSoft, a Sun Microsystems, Inc. business.
      7  * Permission to use, copy, modify, and distribute this
      8  * software is freely granted, provided that this notice
      9  * is preserved.
     10  * ====================================================
     11  */
     12 
     13 #include <sys/cdefs.h>
     14 
     15 #include "namespace.h"
     16 
     17 #include "math.h"
     18 #include "math_private.h"
     19 
     20 #ifdef __weak_alias
     21 __weak_alias(remquof, _remquof)
     22 #endif
     23 
     24 static const float Zero[] = {0.0, -0.0,};
     25 
     26 /*
     27  * Return the IEEE remainder and set *quo to the last n bits of the
     28  * quotient, rounded to the nearest integer.  We choose n=31 because
     29  * we wind up computing all the integer bits of the quotient anyway as
     30  * a side-effect of computing the remainder by the shift and subtract
     31  * method.  In practice, this is far more bits than are needed to use
     32  * remquo in reduction algorithms.
     33  */
     34 float
     35 remquof(float x, float y, int *quo)
     36 {
     37 	int32_t n,hx,hy,hz,ix,iy,sx,i;
     38 	u_int32_t q,sxy;
     39 
     40 	GET_FLOAT_WORD(hx,x);
     41 	GET_FLOAT_WORD(hy,y);
     42 	sxy = (hx ^ hy) & 0x80000000;
     43 	sx = hx&0x80000000;		/* sign of x */
     44 	hx ^=sx;		/* |x| */
     45 	hy &= 0x7fffffff;	/* |y| */
     46 
     47     /* purge off exception values */
     48 	if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
     49 	    return (x*y)/(x*y);
     50 	if(hx<hy) {
     51 	    q = 0;
     52 	    goto fixup;	/* |x|<|y| return x or x-y */
     53 	} else if(hx==hy) {
     54 	    *quo = 1;
     55 	    return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
     56 	}
     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 <<= 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 <<= n;
     80 	}
     81 
     82     /* fix point fmod */
     83 	n = ix - iy;
     84 	q = 0;
     85 	while(n--) {
     86 	    hz=hx-hy;
     87 	    if(hz<0) hx = hx << 1;
     88 	    else {hx = hz << 1; q++;}
     89 	    q <<= 1;
     90 	}
     91 	hz=hx-hy;
     92 	if(hz>=0) {hx=hz;q++;}
     93 
     94     /* convert back to floating value and restore the sign */
     95 	if(hx==0) {				/* return sign(x)*0 */
     96 	    *quo = (sxy ? -q : q);
     97 	    return Zero[(u_int32_t)sx>>31];
     98 	}
     99 	while(hx<0x00800000) {		/* normalize x */
    100 	    hx <<= 1;
    101 	    iy -= 1;
    102 	}
    103 	if(iy>= -126) {		/* normalize output */
    104 	    hx = ((hx-0x00800000)|((iy+127)<<23));
    105 	} else {		/* subnormal output */
    106 	    n = -126 - iy;
    107 	    hx >>= n;
    108 	}
    109 fixup:
    110 	SET_FLOAT_WORD(x,hx);
    111 	y = fabsf(y);
    112 	if (y < 0x1p-125f) {
    113 	    if (x+x>y || (x+x==y && (q & 1))) {
    114 		q++;
    115 		x-=y;
    116 	    }
    117 	} else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
    118 	    q++;
    119 	    x-=y;
    120 	}
    121 	GET_FLOAT_WORD(hx,x);
    122 	SET_FLOAT_WORD(x,hx^sx);
    123 	q &= 0x7fffffff;
    124 	*quo = (sxy ? -q : q);
    125 	return x;
    126 }
    127