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
  13 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_nextafter.c,v 1.11 2002/05/26 22:01:57 wiz Exp $");
  16 #endif
  17
  18 /* IEEE functions
  19  *      nextafter(x,y)
  20  *      return the next machine floating-point number of x in the
  21  *      direction toward y.
  22  *   Special cases:
  23  */
  24
  25 #include "math.h"
  26 #include "math_private.h"
  27
  28 double
  29 nextafter(double x, double y)
  30 {
  31         int32_t hx,hy,ix,iy;
  32         u_int32_t lx,ly;
  33
  34         EXTRACT_WORDS(hx,lx,x);
  35         EXTRACT_WORDS(hy,ly,y);
  36         ix = hx&0x7fffffff;             /* |x| */
  37         iy = hy&0x7fffffff;             /* |y| */
  38
  39         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  40            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  41            return x+y;
  42         if(x==y) return x;              /* x=y, return x */
  43         if((ix|lx)==0) {                        /* x == 0 */
  44             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  45             y = x*x;
  46             if(y==x) return y; else return x;   /* raise underflow flag */
  47         }
  48         if(hx>=0) {                             /* x > 0 */
  49             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  50                 if(lx==0) hx -= 1;
  51                 lx -= 1;
  52             } else {                            /* x < y, x += ulp */
  53                 lx += 1;
  54                 if(lx==0) hx += 1;
  55             }
  56         } else {                                /* x < 0 */
  57             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  58                 if(lx==0) hx -= 1;
  59                 lx -= 1;
  60             } else {                            /* x > y, x += ulp */
  61                 lx += 1;
  62                 if(lx==0) hx += 1;
  63             }
  64         }
  65         hy = hx&0x7ff00000;
  66         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  67         if(hy<0x00100000) {             /* underflow */
  68             y = x*x;
  69             if(y!=x) {          /* raise underflow flag */
  70                 INSERT_WORDS(y,hx,lx);
  71                 return y;
  72             }
  73         }
  74         INSERT_WORDS(x,hx,lx);
  75         return x;
  76 }