lib/libm/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 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_nextafter.c,v 1.14 2014/03/18 18:20:37 riastradh Exp $");
  16 #endif
  17
  18 /* IEEE functions
  19  *      nextafter(x,y)
  20  *      return the next machine floating-point number of x in the
  21  *      direction toward y.
  22  *   Special cases:
  23  */
  24
  25 #include "math.h"
  26 #include "math_private.h"
  27
  28 #ifndef __HAVE_LONG_DOUBLE
  29 __strong_alias(nextafterl, nextafter)
  30 #endif
  31
  32 double
  33 nextafter(double x, double y)
  34 {
  35         int32_t hx,hy,ix,iy;
  36         u_int32_t lx,ly;
  37
  38         EXTRACT_WORDS(hx,lx,x);
  39         EXTRACT_WORDS(hy,ly,y);
  40         ix = hx&0x7fffffff;             /* |x| */
  41         iy = hy&0x7fffffff;             /* |y| */
  42
  43         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  44            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  45            return x+y;
  46         if(x==y) return y;              /* x=y, return y */
  47         if((ix|lx)==0) {                        /* x == 0 */
  48             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  49             y = x*x;
  50             if(y==x) return y; else return x;   /* raise underflow flag */
  51         }
  52         if(hx>=0) {                             /* x > 0 */
  53             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  54                 if(lx==0) hx -= 1;
  55                 lx -= 1;
  56             } else {                            /* x < y, x += ulp */
  57                 lx += 1;
  58                 if(lx==0) hx += 1;
  59             }
  60         } else {                                /* x < 0 */
  61             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  62                 if(lx==0) hx -= 1;
  63                 lx -= 1;
  64             } else {                            /* x > y, x += ulp */
  65                 lx += 1;
  66                 if(lx==0) hx += 1;
  67             }
  68         }
  69         hy = hx&0x7ff00000;
  70         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  71         if(hy<0x00100000) {             /* underflow */
  72             y = x*x;
  73             if(y!=x) {          /* raise underflow flag */
  74                 INSERT_WORDS(y,hx,lx);
  75                 return y;
  76             }
  77         }
  78         INSERT_WORDS(x,hx,lx);
  79         return x;
  80 }