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chore(ricepp): add comment to bitstream_reader

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Marcus Holland-Moritz 2024-02-10 11:11:38 +01:00
parent 3109827ac2
commit 336cce52bf
1 changed files with 6 additions and 0 deletions
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6
ricepp/include/ricepp/bitstream_reader.h
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@ -121,6 +121,12 @@ class bitstream_reader final {
if (bit_pos_ == 0) [[unlikely]] { if (bit_pos_ == 0) [[unlikely]] {
data_ = read_packet(); data_ = read_packet();
} }
// The remainder of this function is equivalent to:
//
// return _bextr_u64(data_, bit_pos_, num_bits);
//
// However, in practice, at least clang generates code that is as fast
// as the intrinsic, so we use the following code for portability.
bits_type bits = data_ >> bit_pos_; bits_type bits = data_ >> bit_pos_;
if (num_bits < kBitsTypeBits) [[likely]] { if (num_bits < kBitsTypeBits) [[likely]] {
bits &= (static_cast<bits_type>(1) << num_bits) - 1; bits &= (static_cast<bits_type>(1) << num_bits) - 1;