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Use absl instead of self-made function for low-level bit counting

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to reduce code duplication and rely on better optimized code.

Bug: None
Change-Id: Ie2f1ff680ff702aae84132229ae0e1743478424f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/229385
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34857}
This commit is contained in:
Danil Chapovalov
2021-08-20 12:46:14 +02:00
committed by WebRTC LUCI CQ
parent c80c566134
commit 09fb787f9a
4 changed files with 9 additions and 15 deletions
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1
DEPS
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@ -2658,6 +2658,7 @@ include_rules = [
"+absl/functional/bind_front.h",
"+absl/memory/memory.h",
"+absl/meta/type_traits.h",
"+absl/numeric/bits.h",
"+absl/strings/ascii.h",
"+absl/strings/match.h",
"+absl/strings/str_replace.h",

1
g3doc/abseil-in-webrtc.md
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@ -41,6 +41,7 @@ will generate a shared library.
* `absl/base/const_init.h` for mutex initialization.
* The macros in `absl/base/attributes.h`, `absl/base/config.h` and
`absl/base/macros.h`.
* `absl/numeric/bits.h`
## **Disallowed**

1
rtc_base/BUILD.gn
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@ -84,6 +84,7 @@ rtc_library("rtc_base_approved") {
]
absl_deps = [
"//third_party/abseil-cpp/absl/base:core_headers",
"//third_party/abseil-cpp/absl/numeric:bits",
"//third_party/abseil-cpp/absl/types:optional",
]
public_deps = [] # no-presubmit-check TODO(webrtc:8603)

21
rtc_base/bit_buffer.cc
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@ -13,6 +13,7 @@
#include <algorithm>
#include <limits>
#include "absl/numeric/bits.h"
#include "rtc_base/checks.h"
namespace {
@ -59,16 +60,6 @@ uint8_t WritePartialByte(uint8_t source,
return (target & ~mask) | (source >> target_bit_offset);
}
// Counts the number of bits used in the binary representation of val.
size_t CountBits(uint64_t val) {
size_t bit_count = 0;
while (val != 0) {
bit_count++;
val >>= 1;
}
return bit_count;
}
} // namespace
namespace rtc {
@ -206,7 +197,7 @@ bool BitBuffer::ReadNonSymmetric(uint32_t num_values, uint32_t& val) {
val = 0;
return true;
}
size_t count_bits = CountBits(num_values);
size_t count_bits = absl::bit_width(num_values);
uint32_t num_min_bits_values = (uint32_t{1} << count_bits) - num_values;
if (!ReadBits(count_bits - 1, val)) {
@ -354,7 +345,7 @@ bool BitBufferWriter::WriteNonSymmetric(uint32_t val, uint32_t num_values) {
// But WriteBits doesn't support writing zero bits.
return true;
}
size_t count_bits = CountBits(num_values);
size_t count_bits = absl::bit_width(num_values);
uint32_t num_min_bits_values = (uint32_t{1} << count_bits) - num_values;
return val < num_min_bits_values
@ -366,7 +357,7 @@ size_t BitBufferWriter::SizeNonSymmetricBits(uint32_t val,
uint32_t num_values) {
RTC_DCHECK_LT(val, num_values);
RTC_DCHECK_LE(num_values, uint32_t{1} << 31);
size_t count_bits = CountBits(num_values);
size_t count_bits = absl::bit_width(num_values);
uint32_t num_min_bits_values = (uint32_t{1} << count_bits) - num_values;
return val < num_min_bits_values ? (count_bits - 1) : count_bits;
@ -380,10 +371,10 @@ bool BitBufferWriter::WriteExponentialGolomb(uint32_t val) {
}
uint64_t val_to_encode = static_cast<uint64_t>(val) + 1;
// We need to write CountBits(val+1) 0s and then val+1. Since val (as a
// We need to write bit_width(val+1) 0s and then val+1. Since val (as a
// uint64_t) has leading zeros, we can just write the total golomb encoded
// size worth of bits, knowing the value will appear last.
return WriteBits(val_to_encode, CountBits(val_to_encode) * 2 - 1);
return WriteBits(val_to_encode, absl::bit_width(val_to_encode) * 2 - 1);
}
bool BitBufferWriter::WriteSignedExponentialGolomb(int32_t val) {