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  1. /*
  2.  * Copyright (c) 1990 James Ashton - Sydney University
  3.  * Copyright (c) 2012 Stefano Sabatini
  4.  *
  5.  * This file is part of FFmpeg.
  6.  *
  7.  * FFmpeg is free software; you can redistribute it and/or
  8.  * modify it under the terms of the GNU Lesser General Public
  9.  * License as published by the Free Software Foundation; either
  10.  * version 2.1 of the License, or (at your option) any later version.
  11.  *
  12.  * FFmpeg is distributed in the hope that it will be useful,
  13.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15.  * Lesser General Public License for more details.
  16.  *
  17.  * You should have received a copy of the GNU Lesser General Public
  18.  * License along with FFmpeg; if not, write to the Free Software
  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20.  */
  21.  
  22. /**
  23.  * @file
  24.  * X-Face common definitions.
  25.  */
  26.  
  27. #include <stdint.h>
  28.  
  29. /* define the face size - 48x48x1 */
  30. #define XFACE_WIDTH  48
  31. #define XFACE_HEIGHT 48
  32. #define XFACE_PIXELS (XFACE_WIDTH * XFACE_HEIGHT)
  33.  
  34. /* compressed output uses the full range of printable characters.
  35.  * In ASCII these are in a contiguous block so we just need to know
  36.  * the first and last. The total number of printables is needed too. */
  37. #define XFACE_FIRST_PRINT '!'
  38. #define XFACE_LAST_PRINT '~'
  39. #define XFACE_PRINTS (XFACE_LAST_PRINT - XFACE_FIRST_PRINT + 1)
  40.  
  41. /*
  42.  * Image is encoded as a big integer, using characters from '~' to
  43.  * '!', for a total of 92 symbols. In order to express 48x48=2304
  44.  * bits, we need a total of 354 digits, as given by:
  45.  * ceil(lg_92(2^2304)) = 354
  46.  */
  47. #define XFACE_MAX_DIGITS 354
  48.  
  49. #define XFACE_BITSPERWORD 8
  50. #define XFACE_WORDCARRY (1 << XFACE_BITSPERWORD)
  51. #define XFACE_WORDMASK (XFACE_WORDCARRY - 1)
  52.  
  53. #define XFACE_MAX_WORDS ((XFACE_PIXELS * 2 + XFACE_BITSPERWORD - 1) / XFACE_BITSPERWORD)
  54.  
  55. /* Portable, very large unsigned integer arithmetic is needed.
  56.  * Implementation uses arrays of WORDs. */
  57. typedef struct {
  58.     int nb_words;
  59.     uint8_t words[XFACE_MAX_WORDS];
  60. } BigInt;
  61.  
  62. /**
  63.  * Add a to b storing the result in b.
  64.  */
  65. void ff_big_add(BigInt *b, uint8_t a);
  66.  
  67. /**
  68.  * Divide b by a storing the result in b and the remainder in the word
  69.  * pointed to by r.
  70.  */
  71. void ff_big_div(BigInt *b, uint8_t a, uint8_t *r);
  72.  
  73. /**
  74.  * Multiply a by b storing the result in b.
  75.  */
  76. void ff_big_mul(BigInt *b, uint8_t a);
  77.  
  78. /* Each face is encoded using 9 octrees of 16x16 each. Each level of the
  79.  * trees has varying probabilities of being white, grey or black.
  80.  * The table below is based on sampling many faces */
  81. enum XFaceColor { XFACE_COLOR_BLACK = 0, XFACE_COLOR_GREY, XFACE_COLOR_WHITE };
  82.  
  83. /* Data of varying probabilities are encoded by a value in the range 0 - 255.
  84.  * The probability of the data determines the range of possible encodings.
  85.  * Offset gives the first possible encoding of the range. */
  86. typedef struct {
  87.     int range;
  88.     int offset;
  89. } ProbRange;
  90.  
  91. extern const ProbRange ff_xface_probranges_per_level[4][3];
  92.  
  93. extern const ProbRange ff_xface_probranges_2x2[16];
  94.  
  95. void ff_xface_generate_face(uint8_t *dst, uint8_t * const src);
  96.