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120 lines
3.5 KiB
120 lines
3.5 KiB
/* Copyright (C) 2005 Ole André Vadla Ravnås <oleavr@gmail.com>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1307 USA
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*/
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#include <string.h>
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#include "mimic-private.h"
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extern guchar _col_zag[64];
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/*
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* _vlc_decode_block
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*
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* De-serialize (reconstruct) a variable length coded 8x8 block.
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*/
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gboolean _vlc_decode_block(MimCtx *ctx, gint *block, gint num_coeffs)
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{
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guint pos;
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memset(block, 0, 64 * sizeof(gint));
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/* The DC-value is read in as is. */
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block[0] = _read_bits(ctx, 8);
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for (pos = 1; pos < num_coeffs; pos++) {
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guint prev_data_index, prev_cur_chunk_len, prev_chunk;
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guint value, num_bits;
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gboolean prev_read_odd, found_magic;
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/* Save context. */
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prev_data_index = ctx->data_index;
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prev_cur_chunk_len = ctx->cur_chunk_len;
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prev_chunk = ctx->cur_chunk;
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prev_read_odd = ctx->read_odd;
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/* Grab 16 bits. */
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value = _read_bits(ctx, 16) << 16;
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/* Restore context. */
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ctx->data_index = prev_data_index;
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ctx->cur_chunk_len = prev_cur_chunk_len;
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ctx->cur_chunk = prev_chunk;
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ctx->read_odd = prev_read_odd;
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/* Analyze and determine number of bits to read initially. */
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num_bits = 3;
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if ((value >> 30) == 0 || (value >> 30) == 1) {
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num_bits = 2;
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} else if ((value & 0xE0000000) != 0x80000000) {
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guint nibble = value >> 28;
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if (nibble == 11 || nibble == 12) {
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num_bits = 4;
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} else if (nibble == 10) {
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_read_bits(ctx, 4);
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return TRUE;
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} else {
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if (((value << 2) & 0x8000000) == 0)
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num_bits = 2;
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num_bits += 2;
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}
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}
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/* Read that number of bits. */
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value = _read_bits(ctx, num_bits);
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/*
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* Look up the current value against the magic ones,
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* and continue extending it bit by bit from the input
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* stream until the magic value is found or we have
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* read 32 bits (in which case we give up).
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*/
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found_magic = FALSE;
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while (!found_magic) {
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VlcMagic *magic;
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if (num_bits > 32)
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return FALSE;
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magic = _find_magic(value);
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if (magic != NULL) {
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pos += magic->pos_add;
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num_bits = magic->num_bits;
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found_magic = TRUE;
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} else {
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value <<= 1;
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value |= _read_bits(ctx, 1);
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num_bits++;
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}
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}
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/* Read the number of bits given by magic value entry. */
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value = _read_bits(ctx, num_bits);
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/* Gotcha! :-) */
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block[_col_zag[pos]] = ctx->vlcdec_lookup[(num_bits * 255) + value];
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}
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return TRUE;
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}
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