| /* |
| * 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); |
| } |