math/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 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_nextafter.c,v 1.8 1995/05/10 20:47:58 jtc 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 /* Ugly hack so that the aliasing works.  */
  25 #define __nexttoward __internal___nexttoward
  26 #define nexttoward __internal_nexttoward
  27
  28 #include <errno.h>
  29 #include <math.h>
  30 #include <math_private.h>
  31 #include <float.h>
  32
  33 double __nextafter(double x, double y)
  34 {
  35         int32_t hx,hy,ix,iy;
  36         u_int32_t lx,ly;
  37
  38         EXTRACT_WORDS(hx,lx,x);
  39         EXTRACT_WORDS(hy,ly,y);
  40         ix = hx&0x7fffffff;             /* |x| */
  41         iy = hy&0x7fffffff;             /* |y| */
  42
  43         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  44            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  45            return x+y;
  46         if(x==y) return y;              /* x=y, return y */
  47         if((ix|lx)==0) {                        /* x == 0 */
  48             double u;
  49             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  50             u = math_opt_barrier (x);
  51             u = u*u;
  52             math_force_eval (u);                /* raise underflow flag */
  53             return x;
  54         }
  55         if(hx>=0) {                             /* x > 0 */
  56             if(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         } else {                                /* x < 0 */
  64             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  65                 if(lx==0) hx -= 1;
  66                 lx -= 1;
  67             } else {                            /* x > y, x += ulp */
  68                 lx += 1;
  69                 if(lx==0) hx += 1;
  70             }
  71         }
  72         hy = hx&0x7ff00000;
  73         if(hy>=0x7ff00000) {
  74           double u = x+x;       /* overflow  */
  75           math_force_eval (u);
  76           __set_errno (ERANGE);
  77         }
  78         if(hy<0x00100000) {
  79             double u = x*x;                     /* underflow */
  80             math_force_eval (u);                /* raise underflow flag */
  81           __set_errno (ERANGE);
  82         }
  83         INSERT_WORDS(x,hx,lx);
  84         return x;
  85 }
  86 weak_alias (__nextafter, nextafter)
  87 #ifdef NO_LONG_DOUBLE
  88 strong_alias (__nextafter, __nextafterl)
  89 weak_alias (__nextafter, nextafterl)
  90 strong_alias (__nextafter, __nexttowardl)
  91 weak_alias (__nexttowardl, nexttowardl)
  92 #undef __nexttoward
  93 strong_alias (__nextafter, __nexttoward)
  94 #undef nexttoward
  95 weak_alias (__nextafter, nexttoward)
  96 #endif