mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-28 21:49:33 +00:00
111 lines
3.0 KiB
C
111 lines
3.0 KiB
C
/* 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 */
|