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author | wolfbeast <mcwerewolf@wolfbeast.com> | 2019-11-10 11:39:27 +0100 |
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committer | wolfbeast <mcwerewolf@wolfbeast.com> | 2019-11-10 11:39:27 +0100 |
commit | 974a481d12bf430891725bd3662876358e57e11a (patch) | |
tree | cad011151456251fef2f1b8d02ef4b4e45fad61a /third_party/aom/aom_dsp/entcode.c | |
parent | 6bd66b1728eeddb058066edda740aaeb2ceaec23 (diff) | |
parent | 736d25cbec4541186ed46c935c117ce4d1c7f3bb (diff) | |
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Merge branch 'master' into js-modules
# Conflicts:
# modules/libpref/init/all.js
Diffstat (limited to 'third_party/aom/aom_dsp/entcode.c')
-rw-r--r-- | third_party/aom/aom_dsp/entcode.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/third_party/aom/aom_dsp/entcode.c b/third_party/aom/aom_dsp/entcode.c new file mode 100644 index 000000000..aad96c6fc --- /dev/null +++ b/third_party/aom/aom_dsp/entcode.c @@ -0,0 +1,49 @@ +/* + * Copyright (c) 2001-2016, Alliance for Open Media. All rights reserved + * + * This source code is subject to the terms of the BSD 2 Clause License and + * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License + * was not distributed with this source code in the LICENSE file, you can + * obtain it at www.aomedia.org/license/software. If the Alliance for Open + * Media Patent License 1.0 was not distributed with this source code in the + * PATENTS file, you can obtain it at www.aomedia.org/license/patent. + */ + +#include "aom_dsp/entcode.h" + +/*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; +} |