/*Daala video codec | |

Copyright (c) 2001-2012 Daala project contributors. All rights reserved. | |

Redistribution and use in source and binary forms, with or without | |

modification, are permitted provided that the following conditions are met: | |

- Redistributions of source code must retain the above copyright notice, this | |

list of conditions and the following disclaimer. | |

- Redistributions in binary form must reproduce the above copyright notice, | |

this list of conditions and the following disclaimer in the documentation | |

and/or other materials provided with the distribution. | |

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" | |

AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |

IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE | |

DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE | |

FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |

DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR | |

SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER | |

CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, | |

OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |

OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.*/ | |

#ifdef HAVE_CONFIG_H | |

#include "./config.h" | |

#endif | |

#include "aom_dsp/entcode.h" | |

/*CDFs for uniform probability distributions of small sizes (2 through 16, | |

inclusive).*/ | |

const uint16_t OD_UNIFORM_CDFS_Q15[135] = { | |

16384, 32768, 10923, 21845, 32768, 8192, 16384, 24576, 32768, 6554, 13107, | |

19661, 26214, 32768, 5461, 10923, 16384, 21845, 27307, 32768, 4681, 9362, | |

14043, 18725, 23406, 28087, 32768, 4096, 8192, 12288, 16384, 20480, 24576, | |

28672, 32768, 3641, 7282, 10923, 14564, 18204, 21845, 25486, 29127, 32768, | |

3277, 6554, 9830, 13107, 16384, 19661, 22938, 26214, 29491, 32768, 2979, | |

5958, 8937, 11916, 14895, 17873, 20852, 23831, 26810, 29789, 32768, 2731, | |

5461, 8192, 10923, 13653, 16384, 19115, 21845, 24576, 27307, 30037, 32768, | |

2521, 5041, 7562, 10082, 12603, 15124, 17644, 20165, 22686, 25206, 27727, | |

30247, 32768, 2341, 4681, 7022, 9362, 11703, 14043, 16384, 18725, 21065, | |

23406, 25746, 28087, 30427, 32768, 2185, 4369, 6554, 8738, 10923, 13107, | |

15292, 17476, 19661, 21845, 24030, 26214, 28399, 30583, 32768, 2048, 4096, | |

6144, 8192, 10240, 12288, 14336, 16384, 18432, 20480, 22528, 24576, 26624, | |

28672, 30720, 32768 | |

}; | |

/*Given the current total integer number of bits used and the current value of | |

rng, computes the fraction number of bits used to OD_BITRES precision. | |

This is used by od_ec_enc_tell_frac() and od_ec_dec_tell_frac(). | |

nbits_total: The number of whole bits currently used, i.e., the value | |

returned by od_ec_enc_tell() or od_ec_dec_tell(). | |

rng: The current value of rng from either the encoder or decoder state. | |

Return: The number of bits scaled by 2**OD_BITRES. | |

This will always be slightly larger than the exact value (e.g., all | |

rounding error is in the positive direction).*/ | |

uint32_t od_ec_tell_frac(uint32_t nbits_total, uint32_t rng) { | |

uint32_t nbits; | |

int l; | |

int i; | |

/*To handle the non-integral number of bits still left in the encoder/decoder | |

state, we compute the worst-case number of bits of val that must be | |

encoded to ensure that the value is inside the range for any possible | |

subsequent bits. | |

The computation here is independent of val itself (the decoder does not | |

even track that value), even though the real number of bits used after | |

od_ec_enc_done() may be 1 smaller if rng is a power of two and the | |

corresponding trailing bits of val are all zeros. | |

If we did try to track that special case, then coding a value with a | |

probability of 1/(1 << n) might sometimes appear to use more than n bits. | |

This may help explain the surprising result that a newly initialized | |

encoder or decoder claims to have used 1 bit.*/ | |

nbits = nbits_total << OD_BITRES; | |

l = 0; | |

for (i = OD_BITRES; i-- > 0;) { | |

int b; | |

rng = rng * rng >> 15; | |

b = (int)(rng >> 16); | |

l = l << 1 | b; | |

rng >>= b; | |

} | |

return nbits - l; | |

} |