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  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. ANSI_SYNOPSIS
  24.        #include <math.h>
  25.        double nextafter(double <[val]>, double <[dir]>);
  26.        float nextafterf(float <[val]>, float <[dir]>);
  27.  
  28. TRAD_SYNOPSIS
  29.        #include <math.h>
  30.  
  31.        double nextafter(<[val]>, <[dir]>)
  32.               double <[val]>;
  33.               double <[exp]>;
  34.  
  35.        float nextafter(<[val]>, <[dir]>)
  36.               float <[val]>;
  37.               float <[dir]>;
  38.  
  39.  
  40. DESCRIPTION
  41. <<nextafter>> returns the double-precision floating-point number
  42. closest to <[val]> in the direction toward <[dir]>.  <<nextafterf>>
  43. performs the same operation in single precision.  For example,
  44. <<nextafter(0.0,1.0)>> returns the smallest positive number which is
  45. representable in double precision.
  46.  
  47. RETURNS
  48. Returns the next closest number to <[val]> in the direction toward
  49. <[dir]>.
  50.  
  51. PORTABILITY
  52.         Neither <<nextafter>> nor <<nextafterf>> is required by ANSI C
  53.         or by the System V Interface Definition (Issue 2).
  54. */
  55.  
  56. /* IEEE functions
  57.  *      nextafter(x,y)
  58.  *      return the next machine floating-point number of x in the
  59.  *      direction toward y.
  60.  *   Special cases:
  61.  */
  62.  
  63. #include "fdlibm.h"
  64.  
  65. #ifndef _DOUBLE_IS_32BITS
  66.  
  67. #ifdef __STDC__
  68.         double nextafter(double x, double y)
  69. #else
  70.         double nextafter(x,y)
  71.         double x,y;
  72. #endif
  73. {
  74.         __int32_t       hx,hy,ix,iy;
  75.         __uint32_t lx,ly;
  76.  
  77.         EXTRACT_WORDS(hx,lx,x);
  78.         EXTRACT_WORDS(hy,ly,y);
  79.         ix = hx&0x7fffffff;             /* |x| */
  80.         iy = hy&0x7fffffff;             /* |y| */
  81.  
  82.         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
  83.            ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
  84.            return x+y;                         
  85.         if(x==y) return x;              /* x=y, return x */
  86.         if((ix|lx)==0) {                        /* x == 0 */
  87.             INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
  88.             y = x*x;
  89.             if(y==x) return y; else return x;   /* raise underflow flag */
  90.         }
  91.         if(hx>=0) {                             /* x > 0 */
  92.             if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
  93.                 if(lx==0) hx -= 1;
  94.                 lx -= 1;
  95.             } else {                            /* x < y, x += ulp */
  96.                 lx += 1;
  97.                 if(lx==0) hx += 1;
  98.             }
  99.         } else {                                /* x < 0 */
  100.             if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
  101.                 if(lx==0) hx -= 1;
  102.                 lx -= 1;
  103.             } else {                            /* x > y, x += ulp */
  104.                 lx += 1;
  105.                 if(lx==0) hx += 1;
  106.             }
  107.         }
  108.         hy = hx&0x7ff00000;
  109.         if(hy>=0x7ff00000) return x+x;  /* overflow  */
  110.         if(hy<0x00100000) {             /* underflow */
  111.             y = x*x;
  112.             if(y!=x) {          /* raise underflow flag */
  113.                 INSERT_WORDS(y,hx,lx);
  114.                 return y;
  115.             }
  116.         }
  117.         INSERT_WORDS(x,hx,lx);
  118.         return x;
  119. }
  120.  
  121. #endif /* _DOUBLE_IS_32BITS */
  122.