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Diffstat (limited to 'media/libaom/src/aom_dsp/entenc.c')
| -rw-r--r-- | media/libaom/src/aom_dsp/entenc.c | 423 |
1 files changed, 423 insertions, 0 deletions
diff --git a/media/libaom/src/aom_dsp/entenc.c b/media/libaom/src/aom_dsp/entenc.c new file mode 100644 index 000000000..a61da263c --- /dev/null +++ b/media/libaom/src/aom_dsp/entenc.c @@ -0,0 +1,423 @@ +/* + * 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 pre-carry 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_window low, + unsigned rng) { + int d; + int c; + int s; + 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; + /*TODO: Right now we flush every time we have at least one byte available. + Instead we should use an od_ec_window and flush right before we're about to + shift bits off the end of the window. + For a 32-bit window this is about the same amount of work, but for a 64-bit + window it should be a fair win.*/ + if (s >= 0) { + uint16_t *buf; + uint32_t storage; + uint32_t offs; + unsigned m; + buf = enc->precarry_buf; + storage = enc->precarry_storage; + offs = enc->offs; + if (offs + 2 > storage) { + storage = 2 * storage + 2; + buf = (uint16_t *)realloc(buf, sizeof(*buf) * storage); + if (buf == NULL) { + enc->error = -1; + enc->offs = 0; + return; + } + enc->precarry_buf = buf; + enc->precarry_storage = storage; + } + c += 16; + m = (1 << c) - 1; + if (s >= 8) { + assert(offs < storage); + buf[offs++] = (uint16_t)(low >> c); + low &= m; + c -= 8; + m >>= 8; + } + assert(offs < storage); + buf[offs++] = (uint16_t)(low >> c); + s = c + d - 24; + low &= m; + enc->offs = offs; + } + 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; + } + enc->precarry_buf = (uint16_t *)malloc(sizeof(*enc->precarry_buf) * size); + enc->precarry_storage = size; + if (size > 0 && enc->precarry_buf == NULL) { + enc->precarry_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->precarry_buf); + 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_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 - CDF_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 - CDF_SHIFT)) + + EC_MIN_PROB * (N - (s - 1)); + v = ((r >> 8) * (uint32_t)(fh >> EC_PROB_SHIFT) >> + (7 - EC_PROB_SHIFT - CDF_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 - CDF_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_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->precarry_buf[0] = + (uint16_t)((enc->precarry_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_window)mask << (16 + enc->cnt))) | + (od_ec_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; + uint16_t *buf; + uint32_t offs; + od_ec_window m; + od_ec_window e; + od_ec_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 + /*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.*/ + l = enc->low; + c = enc->cnt; + s = 10; + m = 0x3FFF; + e = ((l + m) & ~m) | (m + 1); + s += c; + offs = enc->offs; + buf = enc->precarry_buf; + if (s > 0) { + unsigned n; + storage = enc->precarry_storage; + if (offs + ((s + 7) >> 3) > storage) { + storage = storage * 2 + ((s + 7) >> 3); + buf = (uint16_t *)realloc(buf, sizeof(*buf) * storage); + if (buf == NULL) { + enc->error = -1; + return NULL; + } + enc->precarry_buf = buf; + enc->precarry_storage = storage; + } + n = (1 << (c + 16)) - 1; + do { + assert(offs < storage); + buf[offs++] = (uint16_t)(e >> (c + 16)); + e &= n; + s -= 8; + c -= 8; + n >>= 8; + } while (s > 0); + } + /*Make sure there's enough room for the entropy-coded bits.*/ + out = enc->buf; + storage = enc->storage; + c = OD_MAXI((s + 7) >> 3, 0); + if (offs + c > storage) { + storage = offs + c; + out = (unsigned char *)realloc(out, sizeof(*out) * storage); + if (out == NULL) { + enc->error = -1; + return NULL; + } + enc->buf = out; + enc->storage = storage; + } + *nbytes = offs; + /*Perform carry propagation.*/ + assert(offs <= storage); + out = out + storage - offs; + c = 0; + while (offs > 0) { + offs--; + c = buf[offs] + c; + out[offs] = (unsigned char)c; + c >>= 8; + } + /*Note: Unless there's an allocation error, if you keep encoding into the + current buffer and call this function again later, everything will work + just fine (you won't get a new packet out, but you will get a single + buffer with the new data appended to the old). + However, this function is O(N) where N is the amount of data coded so far, + so calling it more than once for a given packet is a bad idea.*/ + 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); +} + +/*Saves a entropy coder checkpoint to dst. + This allows an encoder to reverse a series of entropy coder + decisions if it decides that the information would have been + better coded some other way.*/ +void od_ec_enc_checkpoint(od_ec_enc *dst, const od_ec_enc *src) { + OD_COPY(dst, src, 1); +} + +/*Restores an entropy coder checkpoint saved by od_ec_enc_checkpoint. + This can only be used to restore from checkpoints earlier in the target + state's history: you can not switch backwards and forwards or otherwise + switch to a state which isn't a casual ancestor of the current state. + Restore is also incompatible with patching the initial bits, as the + changes will remain in the restored version.*/ +void od_ec_enc_rollback(od_ec_enc *dst, const od_ec_enc *src) { + unsigned char *buf; + uint32_t storage; + uint16_t *precarry_buf; + uint32_t precarry_storage; + assert(dst->storage >= src->storage); + assert(dst->precarry_storage >= src->precarry_storage); + buf = dst->buf; + storage = dst->storage; + precarry_buf = dst->precarry_buf; + precarry_storage = dst->precarry_storage; + OD_COPY(dst, src, 1); + dst->buf = buf; + dst->storage = storage; + dst->precarry_buf = precarry_buf; + dst->precarry_storage = precarry_storage; +} |