lib/libm/src/s_nextafter.c

   1 /* @(#)s_nextafter.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, 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  * $NetBSD: s_nextafter.c,v 1.12 2011/04/18 15:59:09 drochner Exp $
  13  */
  14
  15 /* IEEE functions
  16  *      nextafter(x,y)
  17  *      return the next machine floating-point number of x in the
  18  *      direction toward y.
  19  *   Special cases:
  20  */
  21
  22 #include <math.h>
  23 #include "math_private.h"
  24
  25 double
  26 nextafter(double x, double y)
  27 {
  28         int32_t hx,hy,ix,iy;
  29         u_int32_t lx,ly;
  30
  31         EXTRACT_WORDS(hx,lx,x);
  32         EXTRACT_WORDS(hy,ly,y);
  33         ix = hx&0x7fffffff;             /* |x| */
  34         iy = hy&0x7fffffff;             /* |y| */
  35
  36         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  37            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  38            return x+y;
  39         if(x==y) return y;              /* x=y, return y */
  40         if((ix|lx)==0) {                        /* x == 0 */
  41             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  42             y = x*x;
  43             if(y==x) return y; else return x;   /* raise underflow flag */
  44         }
  45         if(hx>=0) {                             /* x > 0 */
  46             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  47                 if(lx==0) hx -= 1;
  48                 lx -= 1;
  49             } else {                            /* x < y, x += ulp */
  50                 lx += 1;
  51                 if(lx==0) hx += 1;
  52             }
  53         } else {                                /* x < 0 */
  54             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  55                 if(lx==0) hx -= 1;
  56                 lx -= 1;
  57             } else {                            /* x > y, x += ulp */
  58                 lx += 1;
  59                 if(lx==0) hx += 1;
  60             }
  61         }
  62         hy = hx&0x7ff00000;
  63         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  64         if(hy<0x00100000) {             /* underflow */
  65             y = x*x;
  66             if(y!=x) {          /* raise underflow flag */
  67                 INSERT_WORDS(y,hx,lx);
  68                 return y;
  69             }
  70         }
  71         INSERT_WORDS(x,hx,lx);
  72         return x;
  73 }