sysdeps/i386/fpu/s_nexttoward.c

   1 /* s_nexttoward.c
   2  * Special i387 version
   3  * Conversion from s_nextafter.c by Ulrich Drepper, Cygnus Support,
   4  * drepper@cygnus.com.
   5  */
   6
   7 /*
   8  * ====================================================
   9  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  10  *
  11  * Developed at SunPro, a Sun Microsystems, Inc. business.
  12  * Permission to use, copy, modify, and distribute this
  13  * software is freely granted, provided that this notice
  14  * is preserved.
  15  * ====================================================
  16  */
  17
  18 #if defined(LIBM_SCCS) && !defined(lint)
  19 static char rcsid[] = "$NetBSD: $";
  20 #endif
  21
  22 /* IEEE functions
  23  *      nexttoward(x,y)
  24  *      return the next machine floating-point number of x in the
  25  *      direction toward y.
  26  *   Special cases:
  27  */
  28
  29 #include "math.h"
  30 #include <math_private.h>
  31 #include <float.h>
  32
  33 #ifdef __STDC__
  34         double __nexttoward(double x, long double y)
  35 #else
  36         double __nexttoward(x,y)
  37         double x;
  38         long double y;
  39 #endif
  40 {
  41         int32_t hx,ix,iy;
  42         u_int32_t lx,hy,ly,esy;
  43
  44         EXTRACT_WORDS(hx,lx,x);
  45         GET_LDOUBLE_WORDS(esy,hy,ly,y);
  46         ix = hx&0x7fffffff;             /* |x| */
  47         iy = esy&0x7fff;                /* |y| */
  48
  49         /* Intel's extended format has the normally implicit 1 explicit
  50            present.  Sigh!  */
  51         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  52            ((iy>=0x7fff)&&((hy&0x7fffffff)|ly)!=0))        /* y is nan */
  53            return x+y;
  54         if((long double) x==y) return y;        /* x=y, return y */
  55         if((ix|lx)==0) {                        /* x == 0 */
  56             double u;
  57             INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
  58             u = math_opt_barrier (x);
  59             u = u * u;
  60             math_force_eval (u);                /* raise underflow flag */
  61             return x;
  62         }
  63         if(hx>=0) {                             /* x > 0 */
  64             if (esy>=0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  65                 || (((ix>>20)&0x7ff)==iy-0x3c00
  66                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  67                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  68                             && (lx<<11)>ly)))) {        /* x > y, x -= ulp */
  69                 if(lx==0) hx -= 1;
  70                 lx -= 1;
  71             } else {                            /* x < y, x += ulp */
  72                 lx += 1;
  73                 if(lx==0) hx += 1;
  74             }
  75         } else {                                /* x < 0 */
  76             if (esy<0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  77                 || (((ix>>20)&0x7ff)==iy-0x3c00
  78                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  79                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  80                             && (lx<<11)>ly))))  {/* x < y, x -= ulp */
  81                 if(lx==0) hx -= 1;
  82                 lx -= 1;
  83             } else {                            /* x > y, x += ulp */
  84                 lx += 1;
  85                 if(lx==0) hx += 1;
  86             }
  87         }
  88         hy = hx&0x7ff00000;
  89         if(hy>=0x7ff00000) {
  90           x = x+x;      /* overflow  */
  91           if (FLT_EVAL_METHOD != 0 && FLT_EVAL_METHOD != 1)
  92             /* Force conversion to double.  */
  93             asm ("" : "+m"(x));
  94           return x;
  95         }
  96         if(hy<0x00100000) {
  97             double u = x*x;                     /* underflow */
  98             math_force_eval (u);                /* raise underflow flag */
  99         }
 100         INSERT_WORDS(x,hx,lx);
 101         return x;
 102 }
 103 weak_alias (__nexttoward, nexttoward)
 104 #ifdef NO_LONG_DOUBLE
 105 strong_alias (__nexttoward, __nexttowardl)
 106 weak_alias (__nexttoward, nexttowardl)
 107 #endif