lib/libm/src/s_ilogbl.c

   1 /*      $OpenBSD: s_ilogbl.c,v 1.1 2008/12/09 20:00:35 martynas Exp $   */
   2 /*
   3  * From: @(#)s_ilogb.c 5.1 93/09/24
   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 #include <sys/types.h>
  15 #include <machine/ieee.h>
  16 #include <float.h>
  17 #include <limits.h>
  18 #include <math.h>
  19
  20 int
  21 ilogbl(long double x)
  22 {
  23         struct ieee_ext *p = (struct ieee_ext *)&x;
  24         unsigned long m;
  25         int b;
  26
  27         if (p->ext_exp == 0) {
  28                 if ((p->ext_fracl
  29 #ifdef EXT_FRACLMBITS
  30                         | p->ext_fraclm
  31 #endif /* EXT_FRACLMBITS */
  32 #ifdef EXT_FRACHMBITS
  33                         | p->ext_frachm
  34 #endif /* EXT_FRACHMBITS */
  35                         | p->ext_frach) == 0)
  36                         return (FP_ILOGB0);
  37                 /* denormalized */
  38                 if (p->ext_frach == 0
  39 #ifdef EXT_FRACHMBITS
  40                         && p->ext_frachm == 0
  41 #endif
  42                         ) {
  43                         m = 1lu << (EXT_FRACLBITS - 1);
  44                         for (b = EXT_FRACHBITS; !(p->ext_fracl & m); m >>= 1)
  45                                 b++;
  46 #if defined(EXT_FRACHMBITS) && defined(EXT_FRACLMBITS)
  47                         m = 1lu << (EXT_FRACLMBITS - 1);
  48                         for (b += EXT_FRACHMBITS; !(p->ext_fraclm & m); m >>= 1)
  49                                 b++;
  50 #endif /* defined(EXT_FRACHMBITS) && defined(EXT_FRACLMBITS) */
  51                 } else {
  52                         m = 1lu << (EXT_FRACHBITS - 1);
  53                         for (b = 0; !(p->ext_frach & m); m >>= 1)
  54                                 b++;
  55 #ifdef EXT_FRACHMBITS
  56                         m = 1lu << (EXT_FRACHMBITS - 1);
  57                         for (; !(p->ext_frachm & m); m >>= 1)
  58                                 b++;
  59 #endif /* EXT_FRACHMBITS */
  60                 }
  61 #ifdef EXT_IMPLICIT_NBIT
  62                 b++;
  63 #endif
  64                 return (LDBL_MIN_EXP - b - 1);
  65         } else if (p->ext_exp < (LDBL_MAX_EXP << 1) - 1)
  66                 return (p->ext_exp - LDBL_MAX_EXP + 1);
  67         else if (p->ext_fracl != 0
  68 #ifdef EXT_FRACLMBITS
  69                 || p->ext_fraclm != 0
  70 #endif /* EXT_FRACLMBITS */
  71 #ifdef EXT_FRACHMBITS
  72                 || p->ext_frachm != 0
  73 #endif /* EXT_FRACHMBITS */
  74                 || p->ext_frach != 0)
  75                 return (FP_ILOGBNAN);
  76         else
  77                 return (INT_MAX);
  78 }