libm/s_nextafter.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /* IEEE functions
  13  *      nextafter(x,y)
  14  *      return the next machine floating-point number of x in the
  15  *      direction toward y.
  16  *   Special cases:
  17  */
  18
  19 #include "math.h"
  20 #include "math_private.h"
  21
  22 double nextafter(double x, double y)
  23 {
  24         int32_t hx,hy,ix,iy;
  25         u_int32_t lx,ly;
  26
  27         EXTRACT_WORDS(hx,lx,x);
  28         EXTRACT_WORDS(hy,ly,y);
  29         ix = hx&0x7fffffff;             /* |x| */
  30         iy = hy&0x7fffffff;             /* |y| */
  31
  32         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  33            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  34            return x+y;
  35         if(x==y) return y;              /* x=y, return y */
  36         if((ix|lx)==0) {                        /* x == 0 */
  37             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  38             y = x*x;
  39             if(y==x) return y; else return x;   /* raise underflow flag */
  40         }
  41         if(hx>=0) {                             /* x > 0 */
  42             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  43                 if(lx==0) hx -= 1;
  44                 lx -= 1;
  45             } else {                            /* x < y, x += ulp */
  46                 lx += 1;
  47                 if(lx==0) hx += 1;
  48             }
  49         } else {                                /* x < 0 */
  50             if(hy>=0||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         }
  58         hy = hx&0x7ff00000;
  59         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  60         if(hy<0x00100000) {             /* underflow */
  61             y = x*x;
  62             if(y!=x) {          /* raise underflow flag */
  63                 INSERT_WORDS(y,hx,lx);
  64                 return y;
  65             }
  66         }
  67         INSERT_WORDS(x,hx,lx);
  68         return x;
  69 }
  70 libm_hidden_def(nextafter)
  71 strong_alias_untyped(nextafter, nexttoward)
  72 libm_hidden_def(nexttoward)