lib/libm/src/s_nextafter.c

   1 /* @(#)s_nextafter.c 5.1 93/09/24 */
   2 /* $FreeBSD: head/lib/msun/src/s_nextafter.c 176451 2008-02-22 02:30:36Z das $ */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /* IEEE functions
  15  *      nextafter(x,y)
  16  *      return the next machine floating-point number of x in the
  17  *      direction toward y.
  18  *   Special cases:
  19  */
  20
  21 #include <float.h>
  22
  23 #include "math.h"
  24 #include "math_private.h"
  25
  26 double
  27 nextafter(double x, double y)
  28 {
  29         volatile double t;
  30         int32_t hx,hy,ix,iy;
  31         u_int32_t lx,ly;
  32
  33         EXTRACT_WORDS(hx,lx,x);
  34         EXTRACT_WORDS(hy,ly,y);
  35         ix = hx&0x7fffffff;             /* |x| */
  36         iy = hy&0x7fffffff;             /* |y| */
  37
  38         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  39            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  40            return x+y;
  41         if(x==y) return y;              /* x=y, return y */
  42         if((ix|lx)==0) {                        /* x == 0 */
  43             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  44             t = x*x;
  45             if(t==x) return t; else return x;   /* raise underflow flag */
  46         }
  47         if(hx>=0) {                             /* x > 0 */
  48             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  49                 if(lx==0) hx -= 1;
  50                 lx -= 1;
  51             } else {                            /* x < y, x += ulp */
  52                 lx += 1;
  53                 if(lx==0) hx += 1;
  54             }
  55         } else {                                /* x < 0 */
  56             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  57                 if(lx==0) hx -= 1;
  58                 lx -= 1;
  59             } else {                            /* x > y, x += ulp */
  60                 lx += 1;
  61                 if(lx==0) hx += 1;
  62             }
  63         }
  64         hy = hx&0x7ff00000;
  65         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  66         if(hy<0x00100000) {             /* underflow */
  67             t = x*x;
  68             if(t!=x) {          /* raise underflow flag */
  69                 INSERT_WORDS(y,hx,lx);
  70                 return y;
  71             }
  72         }
  73         INSERT_WORDS(x,hx,lx);
  74         return x;
  75 }
  76
  77 #if (LDBL_MANT_DIG == 53)
  78 __weak_reference(nextafter, nexttoward);
  79 __weak_reference(nextafter, nexttowardl);
  80 __weak_reference(nextafter, nextafterl);
  81 #endif