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+/*
+ * 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.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "./config.h"
+#endif
+
+#include <stdlib.h>
+#include <string.h>
+#include "aom_dsp/entenc.h"
+
+/*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;
+ OD_ASSERT(rng <= 65535U);
+ 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) {
+ OD_ASSERT(offs < storage);
+ buf[offs++] = (uint16_t)(low >> c);
+ low &= m;
+ c -= 8;
+ m >>= 8;
+ }
+ OD_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->end_offs = 0;
+ enc->end_window = 0;
+ enc->nend_bits = 0;
+ 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: The cumulative frequency of all symbols that come before the one to be
+ encoded.
+ fh: The cumulative frequency of all symbols up to and including the one to
+ be encoded.
+ {EC_SMALLMUL} Both values are 32768 minus that.*/
+static void od_ec_encode_q15(od_ec_enc *enc, unsigned fl, unsigned fh) {
+ od_ec_window l;
+ unsigned r;
+ unsigned u;
+ unsigned v;
+ l = enc->low;
+ r = enc->rng;
+ OD_ASSERT(32768U <= r);
+#if CONFIG_EC_SMALLMUL
+ OD_ASSERT(fh < fl);
+ OD_ASSERT(fl <= 32768U);
+ if (fl < 32768U) {
+ u = (r >> 8) * (uint32_t)fl >> 7;
+ v = (r >> 8) * (uint32_t)fh >> 7;
+ l += r - u;
+ r = u - v;
+ } else {
+ r -= (r >> 8) * (uint32_t)fh >> 7;
+ }
+#else
+ OD_ASSERT(fl < fh);
+ OD_ASSERT(fh <= 32768U);
+ u = fl * (uint32_t)r >> 15;
+ v = fh * (uint32_t)r >> 15;
+ r = v - u;
+ l += u;
+#endif
+ od_ec_enc_normalize(enc, l, r);
+#if OD_MEASURE_EC_OVERHEAD
+ enc->entropy -= OD_LOG2((double)(OD_ICDF(fh) - OD_ICDF(fl)) / 32768.);
+ enc->nb_symbols++;
+#endif
+}
+
+/*Encode a single binary value.
+ val: The value to encode (0 or 1).
+ {EC_SMALLMUL} f: The probability that the val is one, scaled by 32768.
+ {else} f: The probability that val is zero, 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;
+ OD_ASSERT(0 < f);
+ OD_ASSERT(f < 32768U);
+ l = enc->low;
+ r = enc->rng;
+ OD_ASSERT(32768U <= r);
+#if CONFIG_EC_SMALLMUL
+ v = (r >> 8) * (uint32_t)f >> 7;
+ if (val) l += r - v;
+ r = val ? v : r - v;
+#else
+ v = f * (uint32_t)r >> 15;
+ if (val) l += v;
+ r = val ? r - v : v;
+#endif
+ od_ec_enc_normalize(enc, l, r);
+#if OD_MEASURE_EC_OVERHEAD
+ enc->entropy -=
+ OD_LOG2((double)(val ? 32768 - OD_ICDF(f) : OD_ICDF(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.
+ cdf: The CDF, such that symbol s falls in the range
+ [s > 0 ? cdf[s - 1] : 0, cdf[s]).
+ The values must be monotonically non-decreasing, and the last value
+ must be exactly 32768.
+ 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 *cdf,
+ int nsyms) {
+ (void)nsyms;
+ OD_ASSERT(s >= 0);
+ OD_ASSERT(s < nsyms);
+ OD_ASSERT(cdf[nsyms - 1] == OD_ICDF(32768U));
+ od_ec_encode_q15(enc, s > 0 ? cdf[s - 1] : OD_ICDF(0), cdf[s]);
+}
+
+#if CONFIG_RAWBITS
+/*Encodes a sequence of raw bits in the stream.
+ fl: The bits to encode.
+ ftb: The number of bits to encode.
+ This must be between 0 and 25, inclusive.*/
+void od_ec_enc_bits(od_ec_enc *enc, uint32_t fl, unsigned ftb) {
+ od_ec_window end_window;
+ int nend_bits;
+ OD_ASSERT(ftb <= 25);
+ OD_ASSERT(fl < (uint32_t)1 << ftb);
+#if OD_MEASURE_EC_OVERHEAD
+ enc->entropy += ftb;
+#endif
+ end_window = enc->end_window;
+ nend_bits = enc->nend_bits;
+ if (nend_bits + ftb > OD_EC_WINDOW_SIZE) {
+ unsigned char *buf;
+ uint32_t storage;
+ uint32_t end_offs;
+ buf = enc->buf;
+ storage = enc->storage;
+ end_offs = enc->end_offs;
+ if (end_offs + (OD_EC_WINDOW_SIZE >> 3) >= storage) {
+ unsigned char *new_buf;
+ uint32_t new_storage;
+ new_storage = 2 * storage + (OD_EC_WINDOW_SIZE >> 3);
+ new_buf = (unsigned char *)malloc(sizeof(*new_buf) * new_storage);
+ if (new_buf == NULL) {
+ enc->error = -1;
+ enc->end_offs = 0;
+ return;
+ }
+ OD_COPY(new_buf + new_storage - end_offs, buf + storage - end_offs,
+ end_offs);
+ storage = new_storage;
+ free(buf);
+ enc->buf = buf = new_buf;
+ enc->storage = storage;
+ }
+ do {
+ OD_ASSERT(end_offs < storage);
+ buf[storage - ++end_offs] = (unsigned char)end_window;
+ end_window >>= 8;
+ nend_bits -= 8;
+ } while (nend_bits >= 8);
+ enc->end_offs = end_offs;
+ }
+ OD_ASSERT(nend_bits + ftb <= OD_EC_WINDOW_SIZE);
+ end_window |= (od_ec_window)fl << nend_bits;
+ nend_bits += ftb;
+ enc->end_window = end_window;
+ enc->nend_bits = nend_bits;
+}
+#endif
+
+/*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;
+ OD_ASSERT(nbits >= 0);
+ OD_ASSERT(nbits <= 8);
+ OD_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;
+ uint32_t end_offs;
+ int nend_bits;
+ od_ec_window m;
+ od_ec_window e;
+ od_ec_window l;
+ unsigned r;
+ 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;
+ r = enc->rng;
+ c = enc->cnt;
+ s = 9;
+ m = 0x7FFF;
+ e = (l + m) & ~m;
+ while ((e | m) >= l + r) {
+ s++;
+ m >>= 1;
+ e = (l + m) & ~m;
+ }
+ 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 {
+ OD_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 and the raw
+ bits.*/
+ out = enc->buf;
+ storage = enc->storage;
+ end_offs = enc->end_offs;
+ e = enc->end_window;
+ nend_bits = enc->nend_bits;
+ s = -s;
+ c = OD_MAXI((nend_bits - s + 7) >> 3, 0);
+ if (offs + end_offs + c > storage) {
+ storage = offs + end_offs + c;
+ out = (unsigned char *)realloc(out, sizeof(*out) * storage);
+ if (out == NULL) {
+ enc->error = -1;
+ return NULL;
+ }
+ OD_MOVE(out + storage - end_offs, out + enc->storage - end_offs, end_offs);
+ enc->buf = out;
+ enc->storage = storage;
+ }
+ /*If we have buffered raw bits, flush them as well.*/
+ while (nend_bits > s) {
+ OD_ASSERT(end_offs < storage);
+ out[storage - ++end_offs] = (unsigned char)e;
+ e >>= 8;
+ nend_bits -= 8;
+ }
+ *nbytes = offs + end_offs;
+ /*Perform carry propagation.*/
+ OD_ASSERT(offs + end_offs <= storage);
+ out = out + storage - (offs + end_offs);
+ c = 0;
+ end_offs = offs;
+ while (offs > 0) {
+ offs--;
+ c = buf[offs] + c;
+ out[offs] = (unsigned char)c;
+ c >>= 8;
+ }
+ /*Add any remaining raw bits to the last byte.
+ There is guaranteed to be enough room, because nend_bits <= s.*/
+ OD_ASSERT(nend_bits <= 0 || end_offs > 0);
+ if (nend_bits > 0) out[end_offs - 1] |= (unsigned char)e;
+ /*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->offs + enc->end_offs) * 8 + enc->cnt + enc->nend_bits + 10;
+}
+
+/*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;
+ OD_ASSERT(dst->storage >= src->storage);
+ OD_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;
+}