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/* 2009 for Newlib: Sun's s_ilogb.c converted to be s_logb.c. */
/* @(#)s_ilogb.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
/*
FUNCTION
<<logb>>, <<logbf>>--get exponent of floating-point number
INDEX
logb
INDEX
logbf
ANSI_SYNOPSIS
#include <math.h>
double logb(double <[x]>);
float logbf(float <[x]>);
DESCRIPTION
The <<logb>> functions extract the exponent of <[x]>, as a signed integer value
in floating-point format. If <[x]> is subnormal it is treated as though it were
normalized; thus, for positive finite <[x]>,
@ifnottex
1 <= (<[x]> * FLT_RADIX to the power (-logb(<[x]>))) < FLT_RADIX.
@end ifnottex
@tex
$1 \leq ( x \cdot FLT\_RADIX ^ {-logb(x)} ) < FLT\_RADIX$.
@end tex
A domain error may occur if the argument is zero.
In this floating-point implementation, FLT_RADIX is 2. Which also means
that for finite <[x]>, <<logb>>(<[x]>) = <<floor>>(<<log2>>(<<fabs>>(<[x]>))).
All nonzero, normal numbers can be described as
@ifnottex
<[m]> * 2**<[p]>, where 1.0 <= <[m]> < 2.0.
@end ifnottex
@tex
$m \cdot 2^p$, where $1.0 \leq m < 2.0$.
@end tex
The <<logb>> functions examine the argument <[x]>, and return <[p]>.
The <<frexp>> functions are similar to the <<logb>> functions, but
returning <[m]> adjusted to the interval [.5, 1) or 0, and <[p]>+1.
RETURNS
@comment Formatting note: "$@" forces a new line
When <[x]> is:@*
+inf or -inf, +inf is returned;@*
NaN, NaN is returned;@*
0, -inf is returned, and the divide-by-zero exception is raised;@*
otherwise, the <<logb>> functions return the signed exponent of <[x]>.
PORTABILITY
ANSI C, POSIX
SEEALSO
frexp, ilogb
*/
/* double logb(double x)
* return the binary exponent of non-zero x
* logb(0) = -inf, raise divide-by-zero floating point exception
* logb(+inf|-inf) = +inf (no signal is raised)
* logb(NaN) = NaN (no signal is raised)
* Per C99 recommendation, a NaN argument is returned unchanged.
*/
#include "fdlibm.h"
#ifndef _DOUBLE_IS_32BITS
double
#ifdef __STDC__
logb(double x)
#else
logb(x)
double x;
#endif
{
__int32_t hx,lx,ix;
EXTRACT_WORDS(hx,lx,x);
hx &= 0x7fffffff; /* high |x| */
if(hx<0x00100000) { /* 0 or subnormal */
if((hx|lx)==0) {
double xx;
/* arg==0: return -inf and raise divide-by-zero exception */
INSERT_WORDS(xx,hx,lx); /* +0.0 */
return -1./xx; /* logb(0) = -inf */
}
else /* subnormal x */
if(hx==0) {
for (ix = -1043; lx>0; lx<<=1) ix -=1;
} else {
for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
}
return (double) ix;
}
else if (hx<0x7ff00000) return (hx>>20)-1023; /* normal # */
else if (hx>0x7ff00000 || lx) return x; /* x==NaN */
else return HUGE_VAL; /* x==inf (+ or -) */
}
#endif /* _DOUBLE_IS_32BITS */
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