lib/libm/src/s_nextafterl.c

   1 /*      $NetBSD: s_nextafterl.c,v 1.2 2010/09/17 20:39:39 christos Exp $        */
   2
   3 /* @(#)s_nextafter.c 5.1 93/09/24 */
   4 /*
   5  * ====================================================
   6  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   7  *
   8  * Developed at SunPro, a Sun Microsystems, Inc. business.
   9  * Permission to use, copy, modify, and distribute this
  10  * software is freely granted, provided that this notice
  11  * is preserved.
  12  * ====================================================
  13  */
  14
  15 #include <float.h>
  16 #include <math.h>
  17 #include <machine/ieee.h>
  18
  19 #ifdef EXT_EXP_INFNAN
  20 #if LDBL_MAX_EXP != 0x4000
  21 #error "Unsupported long double format"
  22 #endif
  23
  24 /*
  25  * IEEE functions
  26  *      nextafterl(x,y)
  27  *      return the next machine floating-point number of x in the
  28  *      direction toward y.
  29  *   Special cases:
  30  *      If x == y, y shall be returned
  31  *      If x or y is NaN, a NaN shall be returned
  32  */
  33 long double
  34 nextafterl(long double x, long double y)
  35 {
  36         volatile long double t;
  37         union ieee_ext_u ux, uy;
  38
  39         ux.extu_ld = x;
  40         uy.extu_ld = y;
  41
  42         if ((ux.extu_exp == EXT_EXP_NAN &&
  43                 ((ux.extu_frach &~ LDBL_NBIT)|ux.extu_fracl) != 0) ||
  44             (uy.extu_exp == EXT_EXP_NAN &&
  45                 ((uy.extu_frach &~ LDBL_NBIT)|uy.extu_fracl) != 0))
  46                 return x+y;                     /* x or y is nan */
  47
  48         if (x == y) return y;                   /* x=y, return y */
  49
  50         if (x == 0.0) {
  51                 ux.extu_frach = 0;              /* return +-minsubnormal */
  52                 ux.extu_fracl = 1;
  53                 ux.extu_sign = uy.extu_sign;
  54                 t = ux.extu_ld * ux.extu_ld;
  55                 if (t == ux.extu_ld)
  56                         return t;
  57                 else
  58                         return ux.extu_ld;      /* raise underflow flag */
  59         }
  60
  61         if ((x>0.0) ^ (x<y)) {                  /* x -= ulp */
  62                 if (ux.extu_fracl == 0) {
  63                         if ((ux.extu_frach & ~LDBL_NBIT) == 0)
  64                                 ux.extu_exp -= 1;
  65                         ux.extu_frach = (ux.extu_frach - 1) |
  66                                         (ux.extu_frach & LDBL_NBIT);
  67                 }
  68                 ux.extu_fracl -= 1;
  69         } else {                                /* x += ulp */
  70                 ux.extu_fracl += 1;
  71                 if (ux.extu_fracl == 0) {
  72                         ux.extu_frach = (ux.extu_frach + 1) |
  73                                         (ux.extu_frach & LDBL_NBIT);
  74                         if ((ux.extu_frach & ~LDBL_NBIT) == 0)
  75                                 ux.extu_exp += 1;
  76                 }
  77         }
  78
  79         if (ux.extu_exp == EXT_EXP_INF)
  80                 return x+x;                     /* overflow  */
  81
  82         if (ux.extu_exp == 0) {                 /* underflow */
  83                 mask_nbit_l(ux);
  84                 t = ux.extu_ld * ux.extu_ld;
  85                 if (t != ux.extu_ld)            /* raise underflow flag */
  86                         return ux.extu_ld;
  87         }
  88
  89         return ux.extu_ld;
  90 }
  91 #endif