toolchain/gcc/newlib/libm/common/s_ilogb.c

   1
   2 /* @(#)s_ilogb.c 5.1 93/09/24 */
   3 /*
   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 /*
  15 FUNCTION
  16        <<ilogb>>, <<ilogbf>>---get exponent of floating-point number
  17 INDEX
  18         ilogb
  19 INDEX
  20         ilogbf
  21
  22 ANSI_SYNOPSIS
  23         #include <math.h>
  24         int ilogb(double <[val]>);
  25         int ilogbf(float <[val]>);
  26
  27 TRAD_SYNOPSIS
  28         #include <math.h>
  29         int ilogb(<[val]>)
  30         double <[val]>;
  31
  32         int ilogbf(<[val]>)
  33         float <[val]>;
  34
  35
  36 DESCRIPTION
  37
  38         All nonzero, normal numbers can be described as <[m]> *
  39         2**<[p]>.  <<ilogb>> and <<ilogbf>> examine the argument
  40         <[val]>, and return <[p]>.  The functions <<frexp>> and
  41         <<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also
  42         return <[m]>.
  43
  44 RETURNS
  45
  46 <<ilogb>> and <<ilogbf>> return the power of two used to form the
  47 floating-point argument.  If <[val]> is <<0>>, they return <<-
  48 INT_MAX>> (<<INT_MAX>> is defined in limits.h).  If <[val]> is
  49 infinite, or NaN, they return <<INT_MAX>>.
  50
  51 PORTABILITY
  52         Neither <<ilogb>> nor <<ilogbf>> is required by ANSI C or by
  53         the System V Interface Definition (Issue 2).  */
  54
  55 /* ilogb(double x)
  56  * return the binary exponent of non-zero x
  57  * ilogb(0) = 0x80000001
  58  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  59  */
  60
  61 #include "fdlibm.h"
  62 #include <limits.h>
  63
  64 #ifndef _DOUBLE_IS_32BITS
  65
  66 #ifdef __STDC__
  67         int ilogb(double x)
  68 #else
  69         int ilogb(x)
  70         double x;
  71 #endif
  72 {
  73         __int32_t hx,lx,ix;
  74
  75         EXTRACT_WORDS(hx,lx,x);
  76         hx &= 0x7fffffff;
  77         if(hx<0x00100000) {
  78             if((hx|lx)==0)
  79                 return - INT_MAX;       /* ilogb(0) = 0x80000001 */
  80             else                        /* subnormal x */
  81                 if(hx==0) {
  82                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  83                 } else {
  84                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  85                 }
  86             return ix;
  87         }
  88         else if (hx<0x7ff00000) return (hx>>20)-1023;
  89         else return INT_MAX;
  90 }
  91
  92 #endif /* _DOUBLE_IS_32BITS */