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/*
* Various fixed-point math operations
*
* Copyright (c) 2008 Vladimir Voroshilov
*
* This file is part of Libav.
*
* Libav is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* Libav is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <inttypes.h>
#include <limits.h>
#include <assert.h>
#include "avcodec.h"
#include "celp_math.h"
#include "libavutil/common.h"
static const uint16_t exp2a[]=
{
0, 1435, 2901, 4400, 5931, 7496, 9096, 10730,
12400, 14106, 15850, 17632, 19454, 21315, 23216, 25160,
27146, 29175, 31249, 33368, 35534, 37747, 40009, 42320,
44682, 47095, 49562, 52082, 54657, 57289, 59979, 62727,
};
static const uint16_t exp2b[]=
{
3, 712, 1424, 2134, 2845, 3557, 4270, 4982,
5696, 6409, 7124, 7839, 8554, 9270, 9986, 10704,
11421, 12138, 12857, 13576, 14295, 15014, 15734, 16455,
17176, 17898, 18620, 19343, 20066, 20790, 21514, 22238,
};
int ff_exp2(uint16_t power)
{
unsigned int result= exp2a[power>>10] + 0x10000;
assert(power <= 0x7fff);
result= (result<<3) + ((result*exp2b[(power>>5)&31])>>17);
return result + ((result*(power&31)*89)>>22);
}
/**
* Table used to compute log2(x)
*
* tab_log2[i] = (1<<15) * log2(1 + i/32), i=0..32
*/
static const uint16_t tab_log2[33] =
{
4, 1459, 2870, 4240, 5572, 6867, 8127, 9355,
10552, 11719, 12858, 13971, 15057, 16120, 17158, 18175,
19170, 20145, 21100, 22036, 22954, 23854, 24738, 25605,
26457, 27294, 28116, 28924, 29719, 30500, 31269, 32025, 32769,
};
int ff_log2(uint32_t value)
{
uint8_t power_int;
uint8_t frac_x0;
uint16_t frac_dx;
// Stripping zeros from beginning
power_int = av_log2(value);
value <<= (31 - power_int);
// b31 is always non-zero now
frac_x0 = (value & 0x7c000000) >> 26; // b26-b31 and [32..63] -> [0..31]
frac_dx = (value & 0x03fff800) >> 11;
value = tab_log2[frac_x0];
value += (frac_dx * (tab_log2[frac_x0+1] - tab_log2[frac_x0])) >> 15;
return (power_int << 15) + value;
}
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