compiler/stdc/math/s_ilogbl.c

   1 /*
   2  * From: @(#)s_ilogb.c 5.1 93/09/24
   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 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ilogbl.c,v 1.1 2004/10/11 18:13:52 stefanf Exp $";
  15 #endif
  16
  17 #include <float.h>
  18 #include <limits.h>
  19 #include <math.h>
  20
  21 #include "fpmath.h"
  22
  23 int
  24 ilogbl(long double x)
  25 {
  26         union IEEEl2bits u;
  27         unsigned long m;
  28         int b;
  29
  30         u.e = x;
  31         if (u.bits.exp == 0) {
  32                 if ((u.bits.manl | u.bits.manh) == 0)
  33                         return (FP_ILOGB0);
  34                 /* denormalized */
  35                 if (u.bits.manh == 0) {
  36                         m = 1lu << (LDBL_MANL_SIZE - 1);
  37                         for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
  38                                 b++;
  39                 } else {
  40                         m = 1lu << (LDBL_MANH_SIZE - 1);
  41                         for (b = 0; !(u.bits.manh & m); m >>= 1)
  42                                 b++;
  43                 }
  44 #ifdef LDBL_IMPLICIT_NBIT
  45                 b++;
  46 #endif
  47                 return (LDBL_MIN_EXP - b - 1);
  48         } else if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)
  49                 return (u.bits.exp - LDBL_MAX_EXP + 1);
  50         else if (u.bits.manl != 0 || u.bits.manh != 0)
  51                 return (FP_ILOGBNAN);
  52         else
  53                 return (INT_MAX);
  54 }