lib/msun/src/s_nextafter.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 #include <sys/cdefs.h>
  14 __FBSDID("$FreeBSD$");
  15
  16 /* IEEE functions
  17  *      nextafter(x,y)
  18  *      return the next machine floating-point number of x in the
  19  *      direction toward y.
  20  *   Special cases:
  21  */
  22
  23 #include <float.h>
  24
  25 #include "math.h"
  26 #include "math_private.h"
  27
  28 double
  29 nextafter(double x, double y)
  30 {
  31         volatile double t;
  32         int32_t hx,hy,ix,iy;
  33         u_int32_t lx,ly;
  34
  35         EXTRACT_WORDS(hx,lx,x);
  36         EXTRACT_WORDS(hy,ly,y);
  37         ix = hx&0x7fffffff;             /* |x| */
  38         iy = hy&0x7fffffff;             /* |y| */
  39
  40         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  41            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  42            return x+y;
  43         if(x==y) return y;              /* x=y, return y */
  44         if((ix|lx)==0) {                        /* x == 0 */
  45             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  46             t = x*x;
  47             if(t==x) return t; else return x;   /* raise underflow flag */
  48         }
  49         if(hx>=0) {                             /* x > 0 */
  50             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  51                 if(lx==0) hx -= 1;
  52                 lx -= 1;
  53             } else {                            /* x < y, x += ulp */
  54                 lx += 1;
  55                 if(lx==0) hx += 1;
  56             }
  57         } else {                                /* x < 0 */
  58             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* 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         }
  66         hy = hx&0x7ff00000;
  67         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  68         if(hy<0x00100000) {             /* underflow */
  69             t = x*x;
  70             if(t!=x) {          /* raise underflow flag */
  71                 INSERT_WORDS(y,hx,lx);
  72                 return y;
  73             }
  74         }
  75         INSERT_WORDS(x,hx,lx);
  76         return x;
  77 }
  78
  79 #if (LDBL_MANT_DIG == 53)
  80 __weak_reference(nextafter, nexttoward);
  81 __weak_reference(nextafter, nexttowardl);
  82 __weak_reference(nextafter, nextafterl);
  83 #endif