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