lib/msun/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
  13 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_nextafter.c,v 1.5 1999/08/28 00:06:53 peter Exp $";
  15 #endif
  16
  17 /* IEEE functions
  18  *      nextafter(x,y)
  19  *      return the next machine floating-point number of x in the
  20  *      direction toward y.
  21  *   Special cases:
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26
  27 #ifdef __STDC__
  28         double nextafter(double x, double y)
  29 #else
  30         double nextafter(x,y)
  31         double x,y;
  32 #endif
  33 {
  34         int32_t hx,hy,ix,iy;
  35         u_int32_t lx,ly;
  36
  37         EXTRACT_WORDS(hx,lx,x);
  38         EXTRACT_WORDS(hy,ly,y);
  39         ix = hx&0x7fffffff;             /* |x| */
  40         iy = hy&0x7fffffff;             /* |y| */
  41
  42         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  43            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  44            return x+y;
  45         if(x==y) return x;              /* x=y, return x */
  46         if((ix|lx)==0) {                        /* x == 0 */
  47             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  48             y = x*x;
  49             if(y==x) return y; else return x;   /* raise underflow flag */
  50         }
  51         if(hx>=0) {                             /* x > 0 */
  52             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  53                 if(lx==0) hx -= 1;
  54                 lx -= 1;
  55             } else {                            /* x < y, x += ulp */
  56                 lx += 1;
  57                 if(lx==0) hx += 1;
  58             }
  59         } else {                                /* x < 0 */
  60             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  61                 if(lx==0) hx -= 1;
  62                 lx -= 1;
  63             } else {                            /* x > y, x += ulp */
  64                 lx += 1;
  65                 if(lx==0) hx += 1;
  66             }
  67         }
  68         hy = hx&0x7ff00000;
  69         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  70         if(hy<0x00100000) {             /* underflow */
  71             y = x*x;
  72             if(y!=x) {          /* raise underflow flag */
  73                 INSERT_WORDS(y,hx,lx);
  74                 return y;
  75             }
  76         }
  77         INSERT_WORDS(x,hx,lx);
  78         return x;
  79 }