cd559bb49a
Based on libcompface code by James Ashton <James.Ashton@anu.edu.au>, and relicensed to LGPL with the author's consent.
96 lines
3.0 KiB
C
96 lines
3.0 KiB
C
/*
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* Copyright (c) 1990 James Ashton - Sydney University
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* Copyright (c) 2012 Stefano Sabatini
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg 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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* FFmpeg 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 FFmpeg; 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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/**
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* @file
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* X-Face common definitions.
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*/
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#include <stdint.h>
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/* define the face size - 48x48x1 */
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#define XFACE_WIDTH 48
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#define XFACE_HEIGHT 48
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#define XFACE_PIXELS (XFACE_WIDTH * XFACE_HEIGHT)
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/* compressed output uses the full range of printable characters.
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* In ASCII these are in a contiguous block so we just need to know
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* the first and last. The total number of printables is needed too. */
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#define XFACE_FIRST_PRINT '!'
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#define XFACE_LAST_PRINT '~'
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#define XFACE_PRINTS (XFACE_LAST_PRINT - XFACE_FIRST_PRINT + 1)
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/*
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* Image is encoded as a big integer, using characters from '~' to
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* '!', for a total of 92 symbols. In order to express 48x48=2304
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* bits, we need a total of 354 digits, as given by:
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* ceil(lg_92(2^2304)) = 354
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*/
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#define XFACE_MAX_DIGITS 354
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#define XFACE_BITSPERWORD 8
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#define XFACE_WORDCARRY (1 << XFACE_BITSPERWORD)
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#define XFACE_WORDMASK (XFACE_WORDCARRY - 1)
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#define XFACE_MAX_WORDS ((XFACE_PIXELS * 2 + XFACE_BITSPERWORD - 1) / XFACE_BITSPERWORD)
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/* Portable, very large unsigned integer arithmetic is needed.
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* Implementation uses arrays of WORDs. */
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typedef struct {
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int nb_words;
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uint8_t words[XFACE_MAX_WORDS];
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} BigInt;
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/**
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* Add a to b storing the result in b.
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*/
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void ff_big_add(BigInt *b, uint8_t a);
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/**
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* Divide b by a storing the result in b and the remainder in the word
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* pointed to by r.
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*/
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void ff_big_div(BigInt *b, uint8_t a, uint8_t *r);
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/**
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* Multiply a by b storing the result in b.
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*/
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void ff_big_mul(BigInt *b, uint8_t a);
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/* Each face is encoded using 9 octrees of 16x16 each. Each level of the
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* trees has varying probabilities of being white, grey or black.
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* The table below is based on sampling many faces */
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enum XFaceColor { XFACE_COLOR_BLACK = 0, XFACE_COLOR_GREY, XFACE_COLOR_WHITE };
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/* Data of varying probabilities are encoded by a value in the range 0 - 255.
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* The probability of the data determines the range of possible encodings.
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* Offset gives the first possible encoding of the range. */
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typedef struct {
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int range;
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int offset;
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} ProbRange;
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extern const ProbRange ff_xface_probranges_per_level[4][3];
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extern const ProbRange ff_xface_probranges_2x2[16];
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void ff_xface_generate_face(uint8_t *dst, uint8_t * const src);
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