48 lines
1.7 KiB
C
48 lines
1.7 KiB
C
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/*
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* Copyright (c) 2023 The WebRTC 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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// This header file includes the inline functions in H265 parser.
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#ifndef COMMON_VIDEO_H265_H265_INLINE_H_
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#define COMMON_VIDEO_H265_H265_INLINE_H_
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#include <stdint.h>
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#include "rtc_base/compile_assert_c.h"
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extern const int8_t kWebRtcVideo_CountLeadingZeros32_Table[64];
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static __inline int WebRtcVideo_CountLeadingZeros32_NotBuiltin(uint32_t n) {
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// Normalize n by rounding up to the nearest number that is a sequence of 0
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// bits followed by a sequence of 1 bits. This number has the same number of
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// leading zeros as the original n. There are exactly 33 such values.
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n |= n >> 1;
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n |= n >> 2;
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n |= n >> 4;
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n |= n >> 8;
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n |= n >> 16;
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// Multiply the modified n with a constant selected (by exhaustive search)
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// such that each of the 33 possible values of n give a product whose 6 most
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// significant bits are unique. Then look up the answer in the table.
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return kWebRtcVideo_CountLeadingZeros32_Table[(n * 0x8c0b2891) >> 26];
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}
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// Returns the number of leading zero bits in the argument.
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static __inline int WebRtcVideo_CountLeadingZeros32(uint32_t n) {
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#ifdef __GNUC__
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RTC_COMPILE_ASSERT(sizeof(unsigned int) == sizeof(uint32_t));
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return n == 0 ? 32 : __builtin_clz(n);
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#else
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return WebRtcVideo_CountLeadingZeros32_NotBuiltin(n);
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#endif
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}
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#endif // COMMON_VIDEO_H265_H265_INLINE_H_
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