vp9_dsubexp.c 3.0 KB

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  1. /*
  2. Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  3. *
  4. * Use of this source code is governed by a BSD-style license
  5. * that can be found in the LICENSE file in the root of the source
  6. * tree. An additional intellectual property rights grant can be found
  7. * in the file PATENTS. All contributing project authors may
  8. * be found in the AUTHORS file in the root of the source tree.
  9. */
  10. #include "vp9/common/vp9_entropy.h"
  11. #include "vp9/decoder/vp9_dsubexp.h"
  12. static int inv_recenter_nonneg(int v, int m) {
  13. if (v > 2 * m)
  14. return v;
  15. return v % 2 ? m - (v + 1) / 2 : m + v / 2;
  16. }
  17. static int decode_uniform(vp9_reader *r) {
  18. const int l = 8;
  19. const int m = (1 << l) - 191;
  20. const int v = vp9_read_literal(r, l - 1);
  21. return v < m ? v : (v << 1) - m + vp9_read_bit(r);
  22. }
  23. static int inv_remap_prob(int v, int m) {
  24. static int inv_map_table[MAX_PROB - 1] = {
  25. 6, 19, 32, 45, 58, 71, 84, 97, 110, 123, 136, 149, 162, 175, 188,
  26. 201, 214, 227, 240, 253, 0, 1, 2, 3, 4, 5, 7, 8, 9, 10,
  27. 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26,
  28. 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
  29. 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59,
  30. 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 73, 74, 75,
  31. 76, 77, 78, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 90, 91,
  32. 92, 93, 94, 95, 96, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107,
  33. 108, 109, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 124,
  34. 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 137, 138, 139, 140,
  35. 141, 142, 143, 144, 145, 146, 147, 148, 150, 151, 152, 153, 154, 155, 156,
  36. 157, 158, 159, 160, 161, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172,
  37. 173, 174, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 189,
  38. 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 202, 203, 204, 205,
  39. 206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 217, 218, 219, 220, 221,
  40. 222, 223, 224, 225, 226, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237,
  41. 238, 239, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252
  42. };
  43. // The clamp is not necessary for conforming VP9 stream, it is added to
  44. // prevent out of bound access for bad input data
  45. v = clamp(v, 0, 253);
  46. v = inv_map_table[v];
  47. m--;
  48. if ((m << 1) <= MAX_PROB) {
  49. return 1 + inv_recenter_nonneg(v + 1, m);
  50. } else {
  51. return MAX_PROB - inv_recenter_nonneg(v + 1, MAX_PROB - 1 - m);
  52. }
  53. }
  54. static int decode_term_subexp(vp9_reader *r) {
  55. if (!vp9_read_bit(r))
  56. return vp9_read_literal(r, 4);
  57. if (!vp9_read_bit(r))
  58. return vp9_read_literal(r, 4) + 16;
  59. if (!vp9_read_bit(r))
  60. return vp9_read_literal(r, 5) + 32;
  61. return decode_uniform(r) + 64;
  62. }
  63. void vp9_diff_update_prob(vp9_reader *r, vp9_prob* p) {
  64. if (vp9_read(r, DIFF_UPDATE_PROB)) {
  65. const int delp = decode_term_subexp(r);
  66. *p = (vp9_prob)inv_remap_prob(delp, *p);
  67. }
  68. }