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 double __nexttoward(double x, long double y)
  34 {
  35         int32_t hx,ix,iy;
  36         u_int32_t lx,hy,ly,esy;
  37
  38         EXTRACT_WORDS(hx,lx,x);
  39         GET_LDOUBLE_WORDS(esy,hy,ly,y);
  40         ix = hx&0x7fffffff;             /* |x| */
  41         iy = esy&0x7fff;                /* |y| */
  42
  43         /* Intel's extended format has the normally implicit 1 explicit
  44            present.  Sigh!  */
  45         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  46            ((iy>=0x7fff)&&((hy&0x7fffffff)|ly)!=0))        /* y is nan */
  47            return x+y;
  48         if((long double) x==y) return y;        /* x=y, return y */
  49         if((ix|lx)==0) {                        /* x == 0 */
  50             double u;
  51             INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
  52             u = math_opt_barrier (x);
  53             u = u * u;
  54             math_force_eval (u);                /* raise underflow flag */
  55             return x;
  56         }
  57         if(hx>=0) {                             /* x > 0 */
  58             if (x > y) {                        /* x -= ulp */
  59                 if(lx==0) hx -= 1;
  60                 lx -= 1;
  61             } else {                            /* x < y, x += ulp */
  62                 lx += 1;
  63                 if(lx==0) hx += 1;
  64             }
  65         } else {                                /* x < 0 */
  66             if (x < y) {                        /* x -= ulp */
  67                 if(lx==0) hx -= 1;
  68                 lx -= 1;
  69             } else {                            /* x > y, x += ulp */
  70                 lx += 1;
  71                 if(lx==0) hx += 1;
  72             }
  73         }
  74         hy = hx&0x7ff00000;
  75         if(hy>=0x7ff00000) {
  76           x = x+x;      /* overflow  */
  77           if (FLT_EVAL_METHOD != 0 && FLT_EVAL_METHOD != 1)
  78             /* Force conversion to double.  */
  79             asm ("" : "+m"(x));
  80           return x;
  81         }
  82         if(hy<0x00100000) {
  83             double u = x*x;                     /* underflow */
  84             math_force_eval (u);                /* raise underflow flag */
  85         }
  86         INSERT_WORDS(x,hx,lx);
  87         return x;
  88 }
  89 weak_alias (__nexttoward, nexttoward)
  90 #ifdef NO_LONG_DOUBLE
  91 strong_alias (__nexttoward, __nexttowardl)
  92 weak_alias (__nexttoward, nexttowardl)
  93 #endif