contrib/openbsd_libm/src/ld80/s_nexttoward.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 /* IEEE functions
  14  *      nexttoward(x,y)
  15  *      return the next machine floating-point number of x in the
  16  *      direction toward y.
  17  *   Special cases:
  18  */
  19
  20 #include <math.h>
  21 #include <float.h>
  22
  23 #include "math_private.h"
  24
  25 double
  26 nexttoward(double x, long double y)
  27 {
  28         int32_t hx,ix,iy;
  29         u_int32_t lx,hy,ly,esy;
  30
  31         EXTRACT_WORDS(hx,lx,x);
  32         GET_LDOUBLE_WORDS(esy,hy,ly,y);
  33         ix = hx&0x7fffffff;             /* |x| */
  34         iy = esy&0x7fff;                /* |y| */
  35
  36         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  37            ((iy>=0x7fff)&&(hy|ly)!=0))          /* y is nan */
  38            return x+y;
  39         if((long double) x==y) return y;        /* x=y, return y */
  40         if((ix|lx)==0) {                        /* x == 0 */
  41             volatile double u;
  42             INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
  43             u = x;
  44             u = u * u;                          /* raise underflow flag */
  45             return x;
  46         }
  47         if(hx>=0) {                             /* x > 0 */
  48             if (esy>=0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  49                 || (((ix>>20)&0x7ff)==iy-0x3c00
  50                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  51                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  52                             && (lx<<11)>ly)))) {        /* x > y, x -= ulp */
  53                 if(lx==0) hx -= 1;
  54                 lx -= 1;
  55             } else {                            /* x < y, x += ulp */
  56                 lx += 1;
  57                 if(lx==0) hx += 1;
  58             }
  59         } else {                                /* x < 0 */
  60             if (esy<0x8000||((ix>>20)&0x7ff)>iy-0x3c00
  61                 || (((ix>>20)&0x7ff)==iy-0x3c00
  62                     && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
  63                         || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
  64                             && (lx<<11)>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           x = x+x;      /* overflow  */
  75           return x;
  76         }
  77         if(hy<0x00100000) {
  78             volatile double u = x*x;            /* underflow */
  79             if(u==x) {
  80                 INSERT_WORDS(x,hx,lx);
  81                 return x;
  82             }
  83         }
  84         INSERT_WORDS(x,hx,lx);
  85         return x;
  86 }