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/* Copyright (C) 2005 Ole André Vadla Ravnås <oleavr@gmail.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <string.h>
#include "mimic-private.h"
extern guchar _col_zag[64];
/*
* _vlc_decode_block
*
* De-serialize (reconstruct) a variable length coded 8x8 block.
*/
gboolean _vlc_decode_block(MimCtx *ctx, gint *block, gint num_coeffs)
{
guint pos;
memset(block, 0, 64 * sizeof(gint));
/* The DC-value is read in as is. */
block[0] = _read_bits(ctx, 8);
for (pos = 1; pos < num_coeffs; pos++) {
guint prev_data_index, prev_cur_chunk_len, prev_chunk;
guint value, num_bits;
gboolean prev_read_odd, found_magic;
/* Save context. */
prev_data_index = ctx->data_index;
prev_cur_chunk_len = ctx->cur_chunk_len;
prev_chunk = ctx->cur_chunk;
prev_read_odd = ctx->read_odd;
/* Grab 16 bits. */
value = _read_bits(ctx, 16) << 16;
/* Restore context. */
ctx->data_index = prev_data_index;
ctx->cur_chunk_len = prev_cur_chunk_len;
ctx->cur_chunk = prev_chunk;
ctx->read_odd = prev_read_odd;
/* Analyze and determine number of bits to read initially. */
num_bits = 3;
if ((value >> 30) == 0 || (value >> 30) == 1) {
num_bits = 2;
} else if ((value & 0xE0000000) != 0x80000000) {
guint nibble = value >> 28;
if (nibble == 11 || nibble == 12) {
num_bits = 4;
} else if (nibble == 10) {
_read_bits(ctx, 4);
return TRUE;
} else {
if (((value << 2) & 0x8000000) == 0)
num_bits = 2;
num_bits += 2;
}
}
/* Read that number of bits. */
value = _read_bits(ctx, num_bits);
/*
* Look up the current value against the magic ones,
* and continue extending it bit by bit from the input
* stream until the magic value is found or we have
* read 32 bits (in which case we give up).
*/
found_magic = FALSE;
while (!found_magic) {
VlcMagic *magic;
if (num_bits > 32)
return FALSE;
magic = _find_magic(value);
if (magic != NULL) {
pos += magic->pos_add;
num_bits = magic->num_bits;
found_magic = TRUE;
} else {
value <<= 1;
value |= _read_bits(ctx, 1);
num_bits++;
}
}
/* Read the number of bits given by magic value entry. */
value = _read_bits(ctx, num_bits);
/* Gotcha! :-) */
block[_col_zag[pos]] = ctx->vlcdec_lookup[(num_bits * 255) + value];
}
return TRUE;
}
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