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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 94 symbols. In order to express
  44.  * 48x48 pixels with the worst case encoding 666 symbols should
  45.  * be sufficient.
  46.  */
  47. #define XFACE_MAX_DIGITS 666
  48.  
  49. #define XFACE_BITSPERWORD 8
  50. #define XFACE_WORDCARRY (1 << XFACE_BITSPERWORD)
  51. #define XFACE_WORDMASK (XFACE_WORDCARRY - 1)
  52.  
  53. // This must be larger or equal to log256(94^XFACE_MAX_DIGITS)
  54. #define XFACE_MAX_WORDS 546
  55.  
  56. /* Portable, very large unsigned integer arithmetic is needed.
  57.  * Implementation uses arrays of WORDs. */
  58. typedef struct {
  59.     int nb_words;
  60.     uint8_t words[XFACE_MAX_WORDS];
  61. } BigInt;
  62.  
  63. /**
  64.  * Add a to b storing the result in b.
  65.  */
  66. void ff_big_add(BigInt *b, uint8_t a);
  67.  
  68. /**
  69.  * Divide b by a storing the result in b and the remainder in the word
  70.  * pointed to by r.
  71.  */
  72. void ff_big_div(BigInt *b, uint8_t a, uint8_t *r);
  73.  
  74. /**
  75.  * Multiply a by b storing the result in b.
  76.  */
  77. void ff_big_mul(BigInt *b, uint8_t a);
  78.  
  79. /* Each face is encoded using 9 octrees of 16x16 each. Each level of the
  80.  * trees has varying probabilities of being white, grey or black.
  81.  * The table below is based on sampling many faces */
  82. enum XFaceColor { XFACE_COLOR_BLACK = 0, XFACE_COLOR_GREY, XFACE_COLOR_WHITE };
  83.  
  84. /* Data of varying probabilities are encoded by a value in the range 0 - 255.
  85.  * The probability of the data determines the range of possible encodings.
  86.  * Offset gives the first possible encoding of the range. */
  87. typedef struct {
  88.     uint8_t range;
  89.     uint8_t offset;
  90. } ProbRange;
  91.  
  92. extern const ProbRange ff_xface_probranges_per_level[4][3];
  93.  
  94. extern const ProbRange ff_xface_probranges_2x2[16];
  95.  
  96. void ff_xface_generate_face(uint8_t *dst, uint8_t * const src);
  97.