newlib/libm/common/s_nextafter.c

   1
   2 /* @(#)s_nextafter.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15 FUNCTION
  16        <<nextafter>>, <<nextafterf>>---get next number
  17
  18 INDEX
  19         nextafter
  20 INDEX
  21         nextafterf
  22
  23 SYNOPSIS
  24        #include <math.h>
  25        double nextafter(double <[val]>, double <[dir]>);
  26        float nextafterf(float <[val]>, float <[dir]>);
  27
  28 DESCRIPTION
  29 <<nextafter>> returns the double-precision floating-point number
  30 closest to <[val]> in the direction toward <[dir]>.  <<nextafterf>>
  31 performs the same operation in single precision.  For example,
  32 <<nextafter(0.0,1.0)>> returns the smallest positive number which is
  33 representable in double precision.
  34
  35 RETURNS
  36 Returns the next closest number to <[val]> in the direction toward
  37 <[dir]>.
  38
  39 PORTABILITY
  40         Neither <<nextafter>> nor <<nextafterf>> is required by ANSI C
  41         or by the System V Interface Definition (Issue 2).
  42 */
  43
  44 /* IEEE functions
  45  *      nextafter(x,y)
  46  *      return the next machine floating-point number of x in the
  47  *      direction toward y.
  48  *   Special cases:
  49  */
  50
  51 #include "fdlibm.h"
  52
  53 #ifndef _DOUBLE_IS_32BITS
  54
  55 #ifdef __STDC__
  56         double nextafter(double x, double y)
  57 #else
  58         double nextafter(x,y)
  59         double x,y;
  60 #endif
  61 {
  62         __int32_t       hx,hy,ix,iy;
  63         __uint32_t lx,ly;
  64
  65         EXTRACT_WORDS(hx,lx,x);
  66         EXTRACT_WORDS(hy,ly,y);
  67         ix = hx&0x7fffffff;             /* |x| */
  68         iy = hy&0x7fffffff;             /* |y| */
  69
  70         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  71            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  72            return x+y;
  73         if(x==y) return y;              /* x=y, return y */
  74         if((ix|lx)==0) {                        /* x == 0 */
  75             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  76             y = x*x;
  77             if(y==x) return y; else return x;   /* raise underflow flag */
  78         }
  79         if(hx>=0) {                             /* x > 0 */
  80             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  81                 if(lx==0) hx -= 1;
  82                 lx -= 1;
  83             } else {                            /* x < y, x += ulp */
  84                 lx += 1;
  85                 if(lx==0) hx += 1;
  86             }
  87         } else {                                /* x < 0 */
  88             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  89                 if(lx==0) hx -= 1;
  90                 lx -= 1;
  91             } else {                            /* x > y, x += ulp */
  92                 lx += 1;
  93                 if(lx==0) hx += 1;
  94             }
  95         }
  96         hy = hx&0x7ff00000;
  97         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  98         if(hy<0x00100000) {             /* underflow */
  99             y = x*x;
 100             if(y!=x) {          /* raise underflow flag */
 101                 INSERT_WORDS(y,hx,lx);
 102                 return y;
 103             }
 104         }
 105         INSERT_WORDS(x,hx,lx);
 106         return x;
 107 }
 108
 109 #endif /* _DOUBLE_IS_32BITS */