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 #include <float.h>
  22
  23 double nextafter(double x, double y)
  24 {
  25         int32_t hx,hy,ix,iy;
  26         u_int32_t lx,ly;
  27
  28         EXTRACT_WORDS(hx,lx,x);
  29         EXTRACT_WORDS(hy,ly,y);
  30         ix = hx&0x7fffffff;             /* |x| */
  31         iy = hy&0x7fffffff;             /* |y| */
  32
  33         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  34            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  35            return x+y;
  36         if(x==y) return y;              /* x=y, return y */
  37         if((ix|lx)==0) {                        /* x == 0 */
  38             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  39             y = x*x;
  40             if(y==x) return y; else return x;   /* raise underflow flag */
  41         }
  42         if(hx>=0) {                             /* x > 0 */
  43             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  44                 if(lx==0) hx -= 1;
  45                 lx -= 1;
  46             } else {                            /* x < y, x += ulp */
  47                 lx += 1;
  48                 if(lx==0) hx += 1;
  49             }
  50         } else {                                /* x < 0 */
  51             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  52                 if(lx==0) hx -= 1;
  53                 lx -= 1;
  54             } else {                            /* x > y, x += ulp */
  55                 lx += 1;
  56                 if(lx==0) hx += 1;
  57             }
  58         }
  59         hy = hx&0x7ff00000;
  60         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  61         if(hy<0x00100000) {             /* underflow */
  62             y = x*x;
  63             if(y!=x) {          /* raise underflow flag */
  64                 INSERT_WORDS(y,hx,lx);
  65                 return y;
  66             }
  67         }
  68         INSERT_WORDS(x,hx,lx);
  69         return x;
  70 }
  71 libm_hidden_def(nextafter)
  72 #if LDBL_MANT_DIG == DBL_MANT_DIG
  73 strong_alias_untyped(nextafter, nexttoward)
  74 libm_hidden_def(nexttoward)
  75 #else
  76 double nexttoward(double x, long double y)
  77 {
  78        return nextafter(x, y);
  79 }
  80 libm_hidden_def(nexttoward)
  81 #endif