mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-15 01:21:06 +00:00
9e97f239ea
Remove the wordsize-64 implementations by merging them into the main dbl-64 directory. The second patch just moves all wordsize-64 files and removes a few wordsize-64 uses in comments and Implies files. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
91 lines
2.9 KiB
C
91 lines
2.9 KiB
C
/* @(#)e_log10.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.
|
|
* ====================================================
|
|
*/
|
|
|
|
/* __ieee754_log10(x)
|
|
* Return the base 10 logarithm of x
|
|
*
|
|
* Method :
|
|
* Let log10_2hi = leading 40 bits of log10(2) and
|
|
* log10_2lo = log10(2) - log10_2hi,
|
|
* ivln10 = 1/log(10) rounded.
|
|
* Then
|
|
* n = ilogb(x),
|
|
* if(n<0) n = n+1;
|
|
* x = scalbn(x,-n);
|
|
* log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
|
|
*
|
|
* Note 1:
|
|
* To guarantee log10(10**n)=n, where 10**n is normal, the rounding
|
|
* mode must set to Round-to-Nearest.
|
|
* Note 2:
|
|
* [1/log(10)] rounded to 53 bits has error .198 ulps;
|
|
* log10 is monotonic at all binary break points.
|
|
*
|
|
* Special cases:
|
|
* log10(x) is NaN with signal if x < 0;
|
|
* log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
|
|
* log10(NaN) is that NaN with no signal;
|
|
* log10(10**N) = N for N=0,1,...,22.
|
|
*
|
|
* Constants:
|
|
* The hexadecimal values are the intended ones for the following constants.
|
|
* The decimal values may be used, provided that the compiler will convert
|
|
* from decimal to binary accurately enough to produce the hexadecimal values
|
|
* shown.
|
|
*/
|
|
|
|
#include <math.h>
|
|
#include <fix-int-fp-convert-zero.h>
|
|
#include <math_private.h>
|
|
#include <stdint.h>
|
|
#include <libm-alias-finite.h>
|
|
|
|
static const double two54 = 1.80143985094819840000e+16; /* 0x4350000000000000 */
|
|
static const double ivln10 = 4.34294481903251816668e-01; /* 0x3FDBCB7B1526E50E */
|
|
static const double log10_2hi = 3.01029995663611771306e-01; /* 0x3FD34413509F6000 */
|
|
static const double log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF311F12B36 */
|
|
|
|
double
|
|
__ieee754_log10 (double x)
|
|
{
|
|
double y, z;
|
|
int64_t i, hx;
|
|
int32_t k;
|
|
|
|
EXTRACT_WORDS64 (hx, x);
|
|
|
|
k = 0;
|
|
if (hx < INT64_C(0x0010000000000000))
|
|
{ /* x < 2**-1022 */
|
|
if (__glibc_unlikely ((hx & UINT64_C(0x7fffffffffffffff)) == 0))
|
|
return -two54 / fabs (x); /* log(+-0)=-inf */
|
|
if (__glibc_unlikely (hx < 0))
|
|
return (x - x) / (x - x); /* log(-#) = NaN */
|
|
k -= 54;
|
|
x *= two54; /* subnormal number, scale up x */
|
|
EXTRACT_WORDS64 (hx, x);
|
|
}
|
|
/* scale up resulted in a NaN number */
|
|
if (__glibc_unlikely (hx >= UINT64_C(0x7ff0000000000000)))
|
|
return x + x;
|
|
k += (hx >> 52) - 1023;
|
|
i = ((uint64_t) k & UINT64_C(0x8000000000000000)) >> 63;
|
|
hx = (hx & UINT64_C(0x000fffffffffffff)) | ((0x3ff - i) << 52);
|
|
y = (double) (k + i);
|
|
if (FIX_INT_FP_CONVERT_ZERO && y == 0.0)
|
|
y = 0.0;
|
|
INSERT_WORDS64 (x, hx);
|
|
z = y * log10_2lo + ivln10 * __ieee754_log (x);
|
|
return z + y * log10_2hi;
|
|
}
|
|
libm_alias_finite (__ieee754_log10, __log10)
|