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 SYNOPSIS
  23         #include <math.h>
  24         int ilogb(double <[val]>);
  25         int ilogbf(float <[val]>);
  26
  27 DESCRIPTION
  28
  29         All nonzero, normal numbers can be described as <[m]> *
  30         2**<[p]>.  <<ilogb>> and <<ilogbf>> examine the argument
  31         <[val]>, and return <[p]>.  The functions <<frexp>> and
  32         <<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also
  33         return <[m]>.
  34
  35 RETURNS
  36
  37 <<ilogb>> and <<ilogbf>> return the power of two used to form the
  38 floating-point argument.
  39 If <[val]> is <<0>>, they return <<FP_ILOGB0>>.
  40 If <[val]> is infinite, they return <<INT_MAX>>.
  41 If <[val]> is NaN, they return <<FP_ILOGBNAN>>.
  42 (<<FP_ILOGB0>> and <<FP_ILOGBNAN>> are defined in math.h, but in turn are
  43 defined as INT_MIN or INT_MAX from limits.h.  The value of FP_ILOGB0 may be
  44 either INT_MIN or -INT_MAX.  The value of FP_ILOGBNAN may be either INT_MAX or
  45 INT_MIN.)
  46
  47 @comment The bugs might not be worth noting, given the mass non-C99/POSIX
  48 @comment behavior of much of the Newlib math library.
  49 @comment BUGS
  50 @comment On errors, errno is not set per C99 and POSIX requirements even if
  51 @comment (math_errhandling & MATH_ERRNO) is non-zero.
  52
  53 PORTABILITY
  54 C99, POSIX
  55 */
  56
  57 /* ilogb(double x)
  58  * return the binary exponent of non-zero x
  59  * ilogb(0) = 0x80000001
  60  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
  61  */
  62
  63 #include <limits.h>
  64 #include "fdlibm.h"
  65
  66 #ifndef _DOUBLE_IS_32BITS
  67
  68 #ifdef __STDC__
  69         int ilogb(double x)
  70 #else
  71         int ilogb(x)
  72         double x;
  73 #endif
  74 {
  75         __int32_t hx,lx,ix;
  76
  77         EXTRACT_WORDS(hx,lx,x);
  78         hx &= 0x7fffffff;
  79         if(hx<0x00100000) {
  80             if((hx|lx)==0)
  81                 return FP_ILOGB0;       /* ilogb(0) = special case error */
  82             else                        /* subnormal x */
  83                 if(hx==0) {
  84                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
  85                 } else {
  86                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
  87                 }
  88             return ix;
  89         }
  90         else if (hx<0x7ff00000) return (hx>>20)-1023;
  91         #if FP_ILOGBNAN != INT_MAX
  92         else if (hx>0x7ff00000) return FP_ILOGBNAN;     /* NAN */
  93         #endif
  94         else return INT_MAX;    /* infinite (or, possibly, NAN) */
  95 }
  96
  97 #endif /* _DOUBLE_IS_32BITS */