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 <errno.h>
  30 #include <math.h>
  31 #include <math-barriers.h>
  32 #include <math_private.h>
  33 #include <float.h>
  34
  35 double __nexttoward(double x, long double y)
  36 {
  37         int32_t hx,ix,iy;
  38         uint32_t lx,hy,ly,esy;
  39
  40         EXTRACT_WORDS(hx,lx,x);
  41         GET_LDOUBLE_WORDS(esy,hy,ly,y);
  42         ix = hx&0x7fffffff;             /* |x| */
  43         iy = esy&0x7fff;                /* |y| */
  44
  45         /* Intel's extended format has the normally implicit 1 explicit
  46            present.  Sigh!  */
  47         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  48            ((iy>=0x7fff)&&((hy&0x7fffffff)|ly)!=0))        /* y is nan */
  49            return x+y;
  50         if((long double) x==y) return y;        /* x=y, return y */
  51         if((ix|lx)==0) {                        /* x == 0 */
  52             double u;
  53             INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
  54             u = math_opt_barrier (x);
  55             u = u * u;
  56             math_force_eval (u);                /* raise underflow flag */
  57             return x;
  58         }
  59         if(hx>=0) {                             /* x > 0 */
  60             if (x > y) {                        /* x -= ulp */
  61                 if(lx==0) hx -= 1;
  62                 lx -= 1;
  63             } else {                            /* x < y, x += ulp */
  64                 lx += 1;
  65                 if(lx==0) hx += 1;
  66             }
  67         } else {                                /* x < 0 */
  68             if (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         }
  76         hy = hx&0x7ff00000;
  77         if(hy>=0x7ff00000) {
  78           double u = x+x;                       /* overflow  */
  79           math_force_eval (u);
  80           __set_errno (ERANGE);
  81         }
  82         if(hy<0x00100000) {
  83             double u = x*x;                     /* underflow */
  84             math_force_eval (u);                /* raise underflow flag */
  85             __set_errno (ERANGE);
  86         }
  87         INSERT_WORDS(x,hx,lx);
  88         return x;
  89 }
  90 weak_alias (__nexttoward, nexttoward)
  91 #ifdef NO_LONG_DOUBLE
  92 strong_alias (__nexttoward, __nexttowardl)
  93 weak_alias (__nexttoward, nexttowardl)
  94 #endif