mirror of https://git.ffmpeg.org/ffmpeg.git
89 lines
2.6 KiB
C
89 lines
2.6 KiB
C
/*
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* Various fixed-point math operations
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*
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* Copyright (c) 2008 Vladimir Voroshilov
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*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <inttypes.h>
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#include <limits.h>
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#include <assert.h>
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#include "avcodec.h"
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#include "celp_math.h"
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#include "libavutil/common.h"
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static const uint16_t exp2a[]=
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{
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0, 1435, 2901, 4400, 5931, 7496, 9096, 10730,
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12400, 14106, 15850, 17632, 19454, 21315, 23216, 25160,
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27146, 29175, 31249, 33368, 35534, 37747, 40009, 42320,
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44682, 47095, 49562, 52082, 54657, 57289, 59979, 62727,
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};
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static const uint16_t exp2b[]=
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{
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3, 712, 1424, 2134, 2845, 3557, 4270, 4982,
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5696, 6409, 7124, 7839, 8554, 9270, 9986, 10704,
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11421, 12138, 12857, 13576, 14295, 15014, 15734, 16455,
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17176, 17898, 18620, 19343, 20066, 20790, 21514, 22238,
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};
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int ff_exp2(uint16_t power)
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{
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unsigned int result= exp2a[power>>10] + 0x10000;
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assert(power <= 0x7fff);
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result= (result<<3) + ((result*exp2b[(power>>5)&31])>>17);
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return result + ((result*(power&31)*89)>>22);
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}
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/**
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* Table used to compute log2(x)
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*
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* tab_log2[i] = (1<<15) * log2(1 + i/32), i=0..32
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*/
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static const uint16_t tab_log2[33] =
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{
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4, 1459, 2870, 4240, 5572, 6867, 8127, 9355,
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10552, 11719, 12858, 13971, 15057, 16120, 17158, 18175,
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19170, 20145, 21100, 22036, 22954, 23854, 24738, 25605,
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26457, 27294, 28116, 28924, 29719, 30500, 31269, 32025, 32769,
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};
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int ff_log2_q15(uint32_t value)
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{
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uint8_t power_int;
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uint8_t frac_x0;
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uint16_t frac_dx;
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// Stripping zeros from beginning
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power_int = av_log2(value);
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value <<= (31 - power_int);
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// b31 is always non-zero now
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frac_x0 = (value & 0x7c000000) >> 26; // b26-b31 and [32..63] -> [0..31]
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frac_dx = (value & 0x03fff800) >> 11;
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value = tab_log2[frac_x0];
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value += (frac_dx * (tab_log2[frac_x0+1] - tab_log2[frac_x0])) >> 15;
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return (power_int << 15) + value;
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}
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