104 строки
3.1 KiB
C
104 строки
3.1 KiB
C
/*
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* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include <stdlib.h>
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#include "./vpx_config.h"
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#include "vpx_dsp/bitreader.h"
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#include "vpx_dsp/prob.h"
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#include "vpx_dsp/vpx_dsp_common.h"
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#include "vpx_ports/mem.h"
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#include "vpx_mem/vpx_mem.h"
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#include "vpx_util/endian_inl.h"
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int vpx_reader_init(vpx_reader *r,
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const uint8_t *buffer,
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size_t size,
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vpx_decrypt_cb decrypt_cb,
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void *decrypt_state) {
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if (size && !buffer) {
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return 1;
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} else {
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r->buffer_end = buffer + size;
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r->buffer = buffer;
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r->value = 0;
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r->count = -8;
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r->range = 255;
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r->decrypt_cb = decrypt_cb;
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r->decrypt_state = decrypt_state;
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vpx_reader_fill(r);
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return vpx_read_bit(r) != 0; // marker bit
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}
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}
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void vpx_reader_fill(vpx_reader *r) {
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const uint8_t *const buffer_end = r->buffer_end;
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const uint8_t *buffer = r->buffer;
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const uint8_t *buffer_start = buffer;
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BD_VALUE value = r->value;
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int count = r->count;
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const size_t bytes_left = buffer_end - buffer;
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const size_t bits_left = bytes_left * CHAR_BIT;
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int shift = BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT);
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if (r->decrypt_cb) {
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size_t n = VPXMIN(sizeof(r->clear_buffer), bytes_left);
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r->decrypt_cb(r->decrypt_state, buffer, r->clear_buffer, (int)n);
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buffer = r->clear_buffer;
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buffer_start = r->clear_buffer;
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}
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if (bits_left > BD_VALUE_SIZE) {
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const int bits = (shift & 0xfffffff8) + CHAR_BIT;
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BD_VALUE nv;
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BD_VALUE big_endian_values;
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memcpy(&big_endian_values, buffer, sizeof(BD_VALUE));
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#if SIZE_MAX == 0xffffffffffffffffULL
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big_endian_values = HToBE64(big_endian_values);
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#else
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big_endian_values = HToBE32(big_endian_values);
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#endif
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nv = big_endian_values >> (BD_VALUE_SIZE - bits);
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count += bits;
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buffer += (bits >> 3);
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value = r->value | (nv << (shift & 0x7));
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} else {
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const int bits_over = (int)(shift + CHAR_BIT - (int)bits_left);
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int loop_end = 0;
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if (bits_over >= 0) {
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count += LOTS_OF_BITS;
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loop_end = bits_over;
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}
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if (bits_over < 0 || bits_left) {
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while (shift >= loop_end) {
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count += CHAR_BIT;
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value |= (BD_VALUE)*buffer++ << shift;
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shift -= CHAR_BIT;
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}
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}
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}
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// NOTE: Variable 'buffer' may not relate to 'r->buffer' after decryption,
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// so we increase 'r->buffer' by the amount that 'buffer' moved, rather than
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// assign 'buffer' to 'r->buffer'.
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r->buffer += buffer - buffer_start;
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r->value = value;
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r->count = count;
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}
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const uint8_t *vpx_reader_find_end(vpx_reader *r) {
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// Find the end of the coded buffer
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while (r->count > CHAR_BIT && r->count < BD_VALUE_SIZE) {
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r->count -= CHAR_BIT;
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r->buffer--;
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}
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return r->buffer;
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}
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