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LibVideo: Read multiple raw bits at once to refill the range decoder

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This will allow BitStream::read_bool() to read more than one bit from
the range-coded bitstream at a time if needed.
This commit is contained in:
Zaggy1024 2022-10-08 20:41:43 -05:00 • committed by Andrew Kaster
parent 13ccde8637
commit 647472b716
1 changed files with 11 additions and 10 deletions
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21
Userland/Libraries/LibVideo/VP9/BitStream.cpp
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@ -5,6 +5,8 @@
* SPDX-License-Identifier: BSD-2-Clause * SPDX-License-Identifier: BSD-2-Clause
*/ */
#include <AK/BuiltinWrappers.h>
#include "BitStream.h" #include "BitStream.h"
namespace Video::VP9 { namespace Video::VP9 {
@ -96,16 +98,15 @@ ErrorOr<bool> BitStream::read_bool(u8 probability)
return_bool = true; return_bool = true;
} }
while (m_bool_range < 128) { if (m_bool_range < 128) {
bool new_bit; u8 bits_to_shift_into_range = count_leading_zeroes(m_bool_range);
if (m_bool_max_bits) {
new_bit = TRY(read_bit()); if (bits_to_shift_into_range > m_bool_max_bits)
m_bool_max_bits--; return Error::from_string_literal("Range decoder is out of data");
} else {
new_bit = false; m_bool_range <<= bits_to_shift_into_range;
} m_bool_value = (m_bool_value << bits_to_shift_into_range) | TRY(read_bits(bits_to_shift_into_range));
m_bool_range *= 2; m_bool_max_bits -= bits_to_shift_into_range;
m_bool_value = (m_bool_value << 1u) + new_bit;
} }
return return_bool; return return_bool;