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
  32 #ifdef __STDC__
  33         double __nexttoward(double x, long double y)
  34 #else
  35         double __nexttoward(x,y)
  36         double x;
  37         long double y;
  38 #endif
  39 {
  40         int32_t hx,ix,iy;
  41         u_int32_t lx,hy,ly,esy;
  42
  43         EXTRACT_WORDS(hx,lx,x);
  44         GET_LDOUBLE_WORDS(esy,hy,ly,y);
  45         ix = hx&0x7fffffff;             /* |x| */
  46         iy = esy&0x7fff;                /* |y| */
  47
  48         /* Intel's extended format has the normally implicit 1 explicit
  49            present.  Sigh!  */
  50         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  51            ((iy>=0x7fff)&&((hy&0x7fffffff)|ly)!=0))        /* y is nan */
  52            return x+y;
  53         if((long double) x==y) return y;        /* x=y, return y */
  54         if((ix|lx)==0) {                        /* x == 0 */
  55             double x2;
  56             INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
  57             x2 = x*x;
  58             if(x2==x) return x2; else return x; /* raise underflow flag */
  59         }
  60         if(hx>=0) {                             /* x > 0 */
  61             if (esy>=0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  62                 || (((ix>>20)&0x7ff)==iy-0x3c00
  63                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  64                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  65                             && (lx<<11)>ly)))) {        /* x > y, x -= ulp */
  66                 if(lx==0) hx -= 1;
  67                 lx -= 1;
  68             } else {                            /* x < y, x += ulp */
  69                 lx += 1;
  70                 if(lx==0) hx += 1;
  71             }
  72         } else {                                /* x < 0 */
  73             if (esy<0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  74                 || (((ix>>20)&0x7ff)==iy-0x3c00
  75                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  76                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  77                             && (lx<<11)>ly))))  {/* x < y, x -= ulp */
  78                 if(lx==0) hx -= 1;
  79                 lx -= 1;
  80             } else {                            /* x > y, x += ulp */
  81                 lx += 1;
  82                 if(lx==0) hx += 1;
  83             }
  84         }
  85         hy = hx&0x7ff00000;
  86         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  87         if(hy<0x00100000) {             /* underflow */
  88             double x2 = x*x;
  89             if(x2!=x) {         /* raise underflow flag */
  90                 INSERT_WORDS(x2,hx,lx);
  91                 return x2;
  92             }
  93         }
  94         INSERT_WORDS(x,hx,lx);
  95         return x;
  96 }
  97 weak_alias (__nexttoward, nexttoward)
  98 #ifdef NO_LONG_DOUBLE
  99 strong_alias (__nexttoward, __nexttowardl)
 100 weak_alias (__nexttoward, nexttowardl)
 101 #endif