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 1.11 2002/05/26 22:01:57 wiz Exp $
  13  * $DragonFly: src/lib/libm/src/s_nextafter.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  14  */
  15
  16 /* IEEE functions
  17  *      nextafter(x,y)
  18  *      return the next machine floating-point number of x in the
  19  *      direction toward y.
  20  *   Special cases:
  21  */
  22
  23 #include <math.h>
  24 #include "math_private.h"
  25
  26 double
  27 nextafter(double x, double y)
  28 {
  29         int32_t hx,hy,ix,iy;
  30         u_int32_t lx,ly;
  31
  32         EXTRACT_WORDS(hx,lx,x);
  33         EXTRACT_WORDS(hy,ly,y);
  34         ix = hx&0x7fffffff;             /* |x| */
  35         iy = hy&0x7fffffff;             /* |y| */
  36
  37         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  38            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  39            return x+y;
  40         if(x==y) return x;              /* x=y, return x */
  41         if((ix|lx)==0) {                        /* x == 0 */
  42             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  43             y = x*x;
  44             if(y==x) return y; else return x;   /* raise underflow flag */
  45         }
  46         if(hx>=0) {                             /* x > 0 */
  47             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  48                 if(lx==0) hx -= 1;
  49                 lx -= 1;
  50             } else {                            /* x < y, x += ulp */
  51                 lx += 1;
  52                 if(lx==0) hx += 1;
  53             }
  54         } else {                                /* x < 0 */
  55             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  56                 if(lx==0) hx -= 1;
  57                 lx -= 1;
  58             } else {                            /* x > y, x += ulp */
  59                 lx += 1;
  60                 if(lx==0) hx += 1;
  61             }
  62         }
  63         hy = hx&0x7ff00000;
  64         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  65         if(hy<0x00100000) {             /* underflow */
  66             y = x*x;
  67             if(y!=x) {          /* raise underflow flag */
  68                 INSERT_WORDS(y,hx,lx);
  69                 return y;
  70             }
  71         }
  72         INSERT_WORDS(x,hx,lx);
  73         return x;
  74 }