|
Packit |
6c4009 |
/* Single-precision log function.
|
|
Packit |
6c4009 |
Copyright (C) 2017-2018 Free Software Foundation, Inc.
|
|
Packit |
6c4009 |
This file is part of the GNU C Library.
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
The GNU C Library is free software; you can redistribute it and/or
|
|
Packit |
6c4009 |
modify it under the terms of the GNU Lesser General Public
|
|
Packit |
6c4009 |
License as published by the Free Software Foundation; either
|
|
Packit |
6c4009 |
version 2.1 of the License, or (at your option) any later version.
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
The GNU C Library is distributed in the hope that it will be useful,
|
|
Packit |
6c4009 |
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
Packit |
6c4009 |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Packit |
6c4009 |
Lesser General Public License for more details.
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
You should have received a copy of the GNU Lesser General Public
|
|
Packit |
6c4009 |
License along with the GNU C Library; if not, see
|
|
Packit |
6c4009 |
<http://www.gnu.org/licenses/>. */
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
#include <math.h>
|
|
Packit |
6c4009 |
#include <stdint.h>
|
|
Packit |
6c4009 |
#include <shlib-compat.h>
|
|
Packit |
6c4009 |
#include <libm-alias-float.h>
|
|
Packit |
6c4009 |
#include "math_config.h"
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
/*
|
|
Packit |
6c4009 |
LOGF_TABLE_BITS = 4
|
|
Packit |
6c4009 |
LOGF_POLY_ORDER = 4
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
ULP error: 0.818 (nearest rounding.)
|
|
Packit |
6c4009 |
Relative error: 1.957 * 2^-26 (before rounding.)
|
|
Packit |
6c4009 |
*/
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
#define T __logf_data.tab
|
|
Packit |
6c4009 |
#define A __logf_data.poly
|
|
Packit |
6c4009 |
#define Ln2 __logf_data.ln2
|
|
Packit |
6c4009 |
#define N (1 << LOGF_TABLE_BITS)
|
|
Packit |
6c4009 |
#define OFF 0x3f330000
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
float
|
|
Packit |
6c4009 |
__logf (float x)
|
|
Packit |
6c4009 |
{
|
|
Packit |
6c4009 |
/* double_t for better performance on targets with FLT_EVAL_METHOD==2. */
|
|
Packit |
6c4009 |
double_t z, r, r2, y, y0, invc, logc;
|
|
Packit |
6c4009 |
uint32_t ix, iz, tmp;
|
|
Packit |
6c4009 |
int k, i;
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
ix = asuint (x);
|
|
Packit |
6c4009 |
#if WANT_ROUNDING
|
|
Packit |
6c4009 |
/* Fix sign of zero with downward rounding when x==1. */
|
|
Packit |
6c4009 |
if (__glibc_unlikely (ix == 0x3f800000))
|
|
Packit |
6c4009 |
return 0;
|
|
Packit |
6c4009 |
#endif
|
|
Packit |
6c4009 |
if (__glibc_unlikely (ix - 0x00800000 >= 0x7f800000 - 0x00800000))
|
|
Packit |
6c4009 |
{
|
|
Packit |
6c4009 |
/* x < 0x1p-126 or inf or nan. */
|
|
Packit |
6c4009 |
if (ix * 2 == 0)
|
|
Packit |
6c4009 |
return __math_divzerof (1);
|
|
Packit |
6c4009 |
if (ix == 0x7f800000) /* log(inf) == inf. */
|
|
Packit |
6c4009 |
return x;
|
|
Packit |
6c4009 |
if ((ix & 0x80000000) || ix * 2 >= 0xff000000)
|
|
Packit |
6c4009 |
return __math_invalidf (x);
|
|
Packit |
6c4009 |
/* x is subnormal, normalize it. */
|
|
Packit |
6c4009 |
ix = asuint (x * 0x1p23f);
|
|
Packit |
6c4009 |
ix -= 23 << 23;
|
|
Packit |
6c4009 |
}
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
/* x = 2^k z; where z is in range [OFF,2*OFF] and exact.
|
|
Packit |
6c4009 |
The range is split into N subintervals.
|
|
Packit |
6c4009 |
The ith subinterval contains z and c is near its center. */
|
|
Packit |
6c4009 |
tmp = ix - OFF;
|
|
Packit |
6c4009 |
i = (tmp >> (23 - LOGF_TABLE_BITS)) % N;
|
|
Packit |
6c4009 |
k = (int32_t) tmp >> 23; /* arithmetic shift */
|
|
Packit |
6c4009 |
iz = ix - (tmp & 0x1ff << 23);
|
|
Packit |
6c4009 |
invc = T[i].invc;
|
|
Packit |
6c4009 |
logc = T[i].logc;
|
|
Packit |
6c4009 |
z = (double_t) asfloat (iz);
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
/* log(x) = log1p(z/c-1) + log(c) + k*Ln2 */
|
|
Packit |
6c4009 |
r = z * invc - 1;
|
|
Packit |
6c4009 |
y0 = logc + (double_t) k * Ln2;
|
|
Packit |
6c4009 |
|
|
Packit |
6c4009 |
/* Pipelined polynomial evaluation to approximate log1p(r). */
|
|
Packit |
6c4009 |
r2 = r * r;
|
|
Packit |
6c4009 |
y = A[1] * r + A[2];
|
|
Packit |
6c4009 |
y = A[0] * r2 + y;
|
|
Packit |
6c4009 |
y = y * r2 + (y0 + r);
|
|
Packit |
6c4009 |
return (float) y;
|
|
Packit |
6c4009 |
}
|
|
Packit |
6c4009 |
#ifndef __logf
|
|
Packit |
6c4009 |
strong_alias (__logf, __ieee754_logf)
|
|
Packit |
6c4009 |
strong_alias (__logf, __logf_finite)
|
|
Packit |
6c4009 |
versioned_symbol (libm, __logf, logf, GLIBC_2_27);
|
|
Packit |
6c4009 |
libm_alias_float_other (__log, log)
|
|
Packit |
6c4009 |
#endif
|