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Diffstat (limited to '')
| -rw-r--r-- | third_party/aom/aom_dsp/entenc.c | 374 |
1 files changed, 374 insertions, 0 deletions
diff --git a/third_party/aom/aom_dsp/entenc.c b/third_party/aom/aom_dsp/entenc.c new file mode 100644 index 0000000000..591e0ad214 --- /dev/null +++ b/third_party/aom/aom_dsp/entenc.c @@ -0,0 +1,374 @@ +/* + * 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 <stdlib.h> +#include <string.h> +#include <math.h> +#include <assert.h> +#include "aom_dsp/entenc.h" +#include "aom_dsp/prob.h" + +#if OD_MEASURE_EC_OVERHEAD +#if !defined(M_LOG2E) +#define M_LOG2E (1.4426950408889634073599246810019) +#endif +#define OD_LOG2(x) (M_LOG2E * log(x)) +#endif // OD_MEASURE_EC_OVERHEAD + +/*A range encoder. + See entdec.c and the references for implementation details \cite{Mar79,MNW98}. + + @INPROCEEDINGS{Mar79, + author="Martin, G.N.N.", + title="Range encoding: an algorithm for removing redundancy from a digitised + message", + booktitle="Video \& Data Recording Conference", + year=1979, + address="Southampton", + month=Jul, + URL="http://www.compressconsult.com/rangecoder/rngcod.pdf.gz" + } + @ARTICLE{MNW98, + author="Alistair Moffat and Radford Neal and Ian H. Witten", + title="Arithmetic Coding Revisited", + journal="{ACM} Transactions on Information Systems", + year=1998, + volume=16, + number=3, + pages="256--294", + month=Jul, + URL="http://researchcommons.waikato.ac.nz/bitstream/handle/10289/78/content.pdf" + }*/ + +/*Takes updated low and range values, renormalizes them so that + 32768 <= rng < 65536 (flushing bytes from low to the output buffer if + necessary), and stores them back in the encoder context. + low: The new value of low. + rng: The new value of the range.*/ +static void od_ec_enc_normalize(od_ec_enc *enc, od_ec_enc_window low, + unsigned rng) { + int d; + int c; + int s; + if (enc->error) return; + c = enc->cnt; + assert(rng <= 65535U); + /*The number of leading zeros in the 16-bit binary representation of rng.*/ + d = 16 - OD_ILOG_NZ(rng); + s = c + d; + + /* We flush every time "low" cannot safely and efficiently accommodate any + more data. Overall, c must not exceed 63 at the time of byte flush out. To + facilitate this, "s" cannot exceed 56-bits because we have to keep 1 byte + for carry. Also, we need to subtract 16 because we want to keep room for + the next symbol worth "d"-bits (max 15). An alternate condition would be if + (e < d), where e = number of leading zeros in "low", indicating there is + not enough rooom to accommodate "rng" worth of "d"-bits in "low". However, + this approach needs additional computations: (i) compute "e", (ii) push + the leading 0x00's as a special case. + */ + if (s >= 40) { // 56 - 16 + unsigned char *out = enc->buf; + uint32_t storage = enc->storage; + uint32_t offs = enc->offs; + if (offs + 8 > storage) { + storage = 2 * storage + 8; + out = (unsigned char *)realloc(out, sizeof(*out) * storage); + if (out == NULL) { + enc->error = -1; + return; + } + enc->buf = out; + enc->storage = storage; + } + // Need to add 1 byte here since enc->cnt always counts 1 byte less + // (enc->cnt = -9) to ensure correct operation + uint8_t num_bytes_ready = (s >> 3) + 1; + + // Update "c" to contain the number of non-ready bits in "low". Since "low" + // has 64-bit capacity, we need to add the (64 - 40) cushion bits and take + // off the number of ready bits. + c += 24 - (num_bytes_ready << 3); + + // Prepare "output" and update "low" + uint64_t output = low >> c; + low = low & (((uint64_t)1 << c) - 1); + + // Prepare data and carry mask + uint64_t mask = (uint64_t)1 << (num_bytes_ready << 3); + uint64_t carry = output & mask; + + mask = mask - 0x01; + output = output & mask; + + // Write data in a single operation + write_enc_data_to_out_buf(out, offs, output, carry, &enc->offs, + num_bytes_ready); + + // Update state of the encoder: enc->cnt to contain the number of residual + // bits + s = c + d - 24; + } + enc->low = low << d; + enc->rng = rng << d; + enc->cnt = s; +} + +/*Initializes the encoder. + size: The initial size of the buffer, in bytes.*/ +void od_ec_enc_init(od_ec_enc *enc, uint32_t size) { + od_ec_enc_reset(enc); + enc->buf = (unsigned char *)malloc(sizeof(*enc->buf) * size); + enc->storage = size; + if (size > 0 && enc->buf == NULL) { + enc->storage = 0; + enc->error = -1; + } +} + +/*Reinitializes the encoder.*/ +void od_ec_enc_reset(od_ec_enc *enc) { + enc->offs = 0; + enc->low = 0; + enc->rng = 0x8000; + /*This is initialized to -9 so that it crosses zero after we've accumulated + one byte + one carry bit.*/ + enc->cnt = -9; + enc->error = 0; +#if OD_MEASURE_EC_OVERHEAD + enc->entropy = 0; + enc->nb_symbols = 0; +#endif +} + +/*Frees the buffers used by the encoder.*/ +void od_ec_enc_clear(od_ec_enc *enc) { free(enc->buf); } + +/*Encodes a symbol given its frequency in Q15. + fl: CDF_PROB_TOP minus the cumulative frequency of all symbols that come + before the one to be encoded. + fh: CDF_PROB_TOP minus the cumulative frequency of all symbols up to and + including the one to be encoded.*/ +static void od_ec_encode_q15(od_ec_enc *enc, unsigned fl, unsigned fh, int s, + int nsyms) { + od_ec_enc_window l; + unsigned r; + unsigned u; + unsigned v; + l = enc->low; + r = enc->rng; + assert(32768U <= r); + assert(fh <= fl); + assert(fl <= 32768U); + assert(7 - EC_PROB_SHIFT >= 0); + const int N = nsyms - 1; + if (fl < CDF_PROB_TOP) { + u = ((r >> 8) * (uint32_t)(fl >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + + EC_MIN_PROB * (N - (s - 1)); + v = ((r >> 8) * (uint32_t)(fh >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + + EC_MIN_PROB * (N - (s + 0)); + l += r - u; + r = u - v; + } else { + r -= ((r >> 8) * (uint32_t)(fh >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)) + + EC_MIN_PROB * (N - (s + 0)); + } + od_ec_enc_normalize(enc, l, r); +#if OD_MEASURE_EC_OVERHEAD + enc->entropy -= OD_LOG2((double)(OD_ICDF(fh) - OD_ICDF(fl)) / CDF_PROB_TOP.); + enc->nb_symbols++; +#endif +} + +/*Encode a single binary value. + val: The value to encode (0 or 1). + f: The probability that the val is one, scaled by 32768.*/ +void od_ec_encode_bool_q15(od_ec_enc *enc, int val, unsigned f) { + od_ec_enc_window l; + unsigned r; + unsigned v; + assert(0 < f); + assert(f < 32768U); + l = enc->low; + r = enc->rng; + assert(32768U <= r); + v = ((r >> 8) * (uint32_t)(f >> EC_PROB_SHIFT) >> (7 - EC_PROB_SHIFT)); + v += EC_MIN_PROB; + if (val) l += r - v; + r = val ? v : r - v; + od_ec_enc_normalize(enc, l, r); +#if OD_MEASURE_EC_OVERHEAD + enc->entropy -= OD_LOG2((double)(val ? f : (32768 - f)) / 32768.); + enc->nb_symbols++; +#endif +} + +/*Encodes a symbol given a cumulative distribution function (CDF) table in Q15. + s: The index of the symbol to encode. + icdf: 32768 minus the CDF, such that symbol s falls in the range + [s > 0 ? (32768 - icdf[s - 1]) : 0, 32768 - icdf[s]). + The values must be monotonically decreasing, and icdf[nsyms - 1] must + be 0. + nsyms: The number of symbols in the alphabet. + This should be at most 16.*/ +void od_ec_encode_cdf_q15(od_ec_enc *enc, int s, const uint16_t *icdf, + int nsyms) { + (void)nsyms; + assert(s >= 0); + assert(s < nsyms); + assert(icdf[nsyms - 1] == OD_ICDF(CDF_PROB_TOP)); + od_ec_encode_q15(enc, s > 0 ? icdf[s - 1] : OD_ICDF(0), icdf[s], s, nsyms); +} + +/*Overwrites a few bits at the very start of an existing stream, after they + have already been encoded. + This makes it possible to have a few flags up front, where it is easy for + decoders to access them without parsing the whole stream, even if their + values are not determined until late in the encoding process, without having + to buffer all the intermediate symbols in the encoder. + In order for this to work, at least nbits bits must have already been encoded + using probabilities that are an exact power of two. + The encoder can verify the number of encoded bits is sufficient, but cannot + check this latter condition. + val: The bits to encode (in the least nbits significant bits). + They will be decoded in order from most-significant to least. + nbits: The number of bits to overwrite. + This must be no more than 8.*/ +void od_ec_enc_patch_initial_bits(od_ec_enc *enc, unsigned val, int nbits) { + int shift; + unsigned mask; + assert(nbits >= 0); + assert(nbits <= 8); + assert(val < 1U << nbits); + shift = 8 - nbits; + mask = ((1U << nbits) - 1) << shift; + if (enc->offs > 0) { + /*The first byte has been finalized.*/ + enc->buf[0] = (unsigned char)((enc->buf[0] & ~mask) | val << shift); + } else if (9 + enc->cnt + (enc->rng == 0x8000) > nbits) { + /*The first byte has yet to be output.*/ + enc->low = (enc->low & ~((od_ec_enc_window)mask << (16 + enc->cnt))) | + (od_ec_enc_window)val << (16 + enc->cnt + shift); + } else { + /*The encoder hasn't even encoded _nbits of data yet.*/ + enc->error = -1; + } +} + +#if OD_MEASURE_EC_OVERHEAD +#include <stdio.h> +#endif + +/*Indicates that there are no more symbols to encode. + All remaining output bytes are flushed to the output buffer. + od_ec_enc_reset() should be called before using the encoder again. + bytes: Returns the size of the encoded data in the returned buffer. + Return: A pointer to the start of the final buffer, or NULL if there was an + encoding error.*/ +unsigned char *od_ec_enc_done(od_ec_enc *enc, uint32_t *nbytes) { + unsigned char *out; + uint32_t storage; + uint32_t offs; + od_ec_enc_window m; + od_ec_enc_window e; + od_ec_enc_window l; + int c; + int s; + if (enc->error) return NULL; +#if OD_MEASURE_EC_OVERHEAD + { + uint32_t tell; + /* Don't count the 1 bit we lose to raw bits as overhead. */ + tell = od_ec_enc_tell(enc) - 1; + fprintf(stderr, "overhead: %f%%\n", + 100 * (tell - enc->entropy) / enc->entropy); + fprintf(stderr, "efficiency: %f bits/symbol\n", + (double)tell / enc->nb_symbols); + } +#endif + + l = enc->low; + c = enc->cnt; + s = 10; + m = 0x3FFF; + e = ((l + m) & ~m) | (m + 1); + s += c; + offs = enc->offs; + + /*Make sure there's enough room for the entropy-coded bits.*/ + out = enc->buf; + storage = enc->storage; + const int s_bits = (s + 7) >> 3; + int b = OD_MAXI(s_bits, 0); + if (offs + b > storage) { + storage = offs + b; + out = (unsigned char *)realloc(out, sizeof(*out) * storage); + if (out == NULL) { + enc->error = -1; + return NULL; + } + enc->buf = out; + enc->storage = storage; + } + + /*We output the minimum number of bits that ensures that the symbols encoded + thus far will be decoded correctly regardless of the bits that follow.*/ + if (s > 0) { + uint64_t n; + n = ((uint64_t)1 << (c + 16)) - 1; + do { + assert(offs < storage); + uint16_t val = (uint16_t)(e >> (c + 16)); + out[offs] = (unsigned char)(val & 0x00FF); + if (val & 0x0100) { + assert(offs > 0); + propagate_carry_bwd(out, offs - 1); + } + offs++; + + e &= n; + s -= 8; + c -= 8; + n >>= 8; + } while (s > 0); + } + *nbytes = offs; + + return out; +} + +/*Returns the number of bits "used" by the encoded symbols so far. + This same number can be computed in either the encoder or the decoder, and is + suitable for making coding decisions. + Warning: The value returned by this function can decrease compared to an + earlier call, even after encoding more data, if there is an encoding error + (i.e., a failure to allocate enough space for the output buffer). + Return: The number of bits. + This will always be slightly larger than the exact value (e.g., all + rounding error is in the positive direction).*/ +int od_ec_enc_tell(const od_ec_enc *enc) { + /*The 10 here counteracts the offset of -9 baked into cnt, and adds 1 extra + bit, which we reserve for terminating the stream.*/ + return (enc->cnt + 10) + enc->offs * 8; +} + +/*Returns the number of bits "used" by the encoded symbols so far. + This same number can be computed in either the encoder or the decoder, and is + suitable for making coding decisions. + Warning: The value returned by this function can decrease compared to an + earlier call, even after encoding more data, if there is an encoding error + (i.e., a failure to allocate enough space for the output buffer). + 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_enc_tell_frac(const od_ec_enc *enc) { + return od_ec_tell_frac(od_ec_enc_tell(enc), enc->rng); +} |