gcc/libquadmath/math/fmodq.c

/* fmodq.c -- __float128 version of e_fmod.c.
 * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
 */
/*
 * ====================================================
 * 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.
 * ====================================================
 */

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

#include "quadmath-imp.h"

static const __float128 one = 1.0, Zero[] = {0.0, -0.0,};

__float128
fmodq (__float128 x, __float128 y)
{
  int64_t n,hx,hy,hz,ix,iy,sx,i;
  uint64_t lx,ly,lz;

  GET_FLT128_WORDS64(hx,lx,x);
  GET_FLT128_WORDS64(hy,ly,y);
  sx = hx&0x8000000000000000ULL;	/* sign of x */
  hx ^=sx;				/* |x| */
  hy &= 0x7fffffffffffffffLL;		/* |y| */

  /* purge off exception values */
  if((hy|ly)==0||(hx>=0x7fff000000000000LL)|| /* y=0,or x not finite */
    ((hy|((ly|-ly)>>63))>0x7fff000000000000LL))	/* 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[(uint64_t)sx>>63];	/* |x|=|y| return x*0*/
  }

  /* determine ix = ilogb(x) */
  if(hx<0x0001000000000000LL) {	/* subnormal x */
      if(hx==0) {
	  for (ix = -16431, i=lx; i>0; i<<=1) ix -=1;
      } else {
	  for (ix = -16382, i=hx<<15; i>0; i<<=1) ix -=1;
      }
  } else ix = (hx>>48)-0x3fff;

  /* determine iy = ilogb(y) */
      if(hy<0x0001000000000000LL) {	/* subnormal y */
	  if(hy==0) {
	      for (iy = -16431, i=ly; i>0; i<<=1) iy -=1;
	  } else {
	      for (iy = -16382, i=hy<<15; i>0; i<<=1) iy -=1;
	  }
      } else iy = (hy>>48)-0x3fff;

  /* set up {hx,lx}, {hy,ly} and align y to x */
      if(ix >= -16382) 
	  hx = 0x0001000000000000LL|(0x0000ffffffffffffLL&hx);
      else {		/* subnormal x, shift x to normal */
	  n = -16382-ix;
	  if(n<=63) {
	      hx = (hx<<n)|(lx>>(64-n));
	      lx <<= n;
	  } else {
	      hx = lx<<(n-64);
	      lx = 0;
	  }
      }
      if(iy >= -16382) 
	  hy = 0x0001000000000000LL|(0x0000ffffffffffffLL&hy);
      else {		/* subnormal y, shift y to normal */
	  n = -16382-iy;
	  if(n<=63) {
	      hy = (hy<<n)|(ly>>(64-n));
	      ly <<= n;
	  } else {
	      hy = ly<<(n-64);
	      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>>63); lx = lx+lx;}
	  else {
	      if((hz|lz)==0) 		/* return sign(x)*0 */
		  return Zero[(uint64_t)sx>>63];
	      hx = hz+hz+(lz>>63); 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[(uint64_t)sx>>63];	
      while(hx<0x0001000000000000LL) {	/* normalize x */
	  hx = hx+hx+(lx>>63); lx = lx+lx;
	  iy -= 1;
      }
      if(iy>= -16382) {	/* normalize output */
	  hx = ((hx-0x0001000000000000LL)|((iy+16383)<<48));
	  SET_FLT128_WORDS64(x,hx|sx,lx);
      } else {		/* subnormal output */
	  n = -16382 - iy;
	  if(n<=48) {
	      lx = (lx>>n)|((uint64_t)hx<<(64-n));
	      hx >>= n;
	  } else if (n<=63) {
	      lx = (hx<<(64-n))|(lx>>n); hx = sx;
	  } else {
	      lx = hx>>(n-64); hx = sx;
	  }
	  SET_FLT128_WORDS64(x,hx|sx,lx);
	  x *= one;		/* create necessary signal */
      }
      return x;		/* exact output */
}