newlib/libm/ld/s_nexttoward.c

   1 /* @(#)s_nextafter.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #include <sys/cdefs.h>
  14 __FBSDID("$FreeBSD$");
  15
  16 /*
  17  * We assume that a long double has a 15-bit exponent.  On systems
  18  * where long double is the same as double, nexttoward() is an alias
  19  * for nextafter(), so we don't use this routine.
  20  */
  21
  22 #include <float.h>
  23
  24 #include "fpmath.h"
  25 #include "math.h"
  26 #include "math_private.h"
  27
  28 #if LDBL_MAX_EXP != 0x4000
  29 #error "Unsupported long double format"
  30 #endif
  31
  32 double
  33 nexttoward(double x, long double y)
  34 {
  35         union IEEEl2bits uy;
  36         volatile double t;
  37         int32_t hx,ix;
  38         u_int32_t lx;
  39
  40         EXTRACT_WORDS(hx,lx,x);
  41         ix = hx&0x7fffffff;             /* |x| */
  42         uy.e = y;
  43
  44         if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||
  45             (uy.bits.exp == 0x7fff &&
  46              ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0))
  47            return x+y;  /* x or y is nan */
  48         if(x==y) return (double)y;              /* x=y, return y */
  49         if(x==0.0) {
  50             INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */
  51             t = x*x;
  52             if(t==x) return t; else return x;   /* raise underflow flag */
  53         }
  54         if(hx>0.0 ^ x < y) {                    /* x -= ulp */
  55             if(lx==0) hx -= 1;
  56             lx -= 1;
  57         } else {                                /* x += ulp */
  58             lx += 1;
  59             if(lx==0) hx += 1;
  60         }
  61         ix = hx&0x7ff00000;
  62         if(ix>=0x7ff00000) return x+x;  /* overflow  */
  63         if(ix<0x00100000) {             /* underflow */
  64             t = x*x;
  65             if(t!=x) {          /* raise underflow flag */
  66                 INSERT_WORDS(x,hx,lx);
  67                 return x;
  68             }
  69         }
  70         INSERT_WORDS(x,hx,lx);
  71         return x;
  72 }