From 1918ad2ae38aa32c74b558b322479a8efdd76363 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Fri, 11 Dec 2020 14:49:17 -0800 Subject: Export of internal Abseil changes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit -- 0bfa836596a9c787a2f0bdc283011dd1f6810c6e by Benjamin Barenblat : Ignore missing CPU frequency on more architectures Linux on MIPS, PA-RISC, RISC-V, and SystemZ doesn’t expose the nominal CPU frequency via /sys, so don’t worry if `NominalCPUFrequency` returns 1.0 on those platforms. Some POWER machines expose the CPU frequency; others do not. Since we can’t predict which type of machine the tests will run on, simply disable testing for `NominalCPUFrequency` on POWER. PiperOrigin-RevId: 347079873 -- 492b6834ed4a07cbc3abccd846f7e37d8c556ee5 by Benjamin Barenblat : Use ABSL_HAVE_THREAD_LOCAL macro instead of copying code Reduce code duplication by checking the ABSL_HAVE_THREAD_LOCAL macro instead of copying code from base/config.h. PiperOrigin-RevId: 347079561 -- 8d656efce4da9cb032094377e58493d98427a536 by Abseil Team : Rollback PiperOrigin-RevId: 347078779 -- 221bc69ec6dd7e2777ffcff6942584f979ef6382 by Abseil Team : Add flag for 'shallow subcord' feature for experimental ring buffer rollout There is a potential trade-off of CPU cost vs over-sharing cord data for subcord of large cords. This flag allows making subcords shallow for ringbuffers (with a potential larger waste of referenced source cords), which allows us to make subcord fast for this apps that do no persist (unmodified / plain copied) sub cords. This change also introduces constants for the default settings, intended to keep the internal cord settings concistent with external flags. PiperOrigin-RevId: 347053271 -- 00a56c24293566734009f6bf2169a83fb37a35ba by Abseil Team : Revert the usage of variant<> in Cord iterator and reader. The introduction of the variant may lead to some missed compiler optimizations. PiperOrigin-RevId: 347053041 -- c7b7b5ed7e3ab46b1e75b80f1a7de0bda26c8f70 by Chris Kennelly : Release library for integer power-of-2 functions and bit counting. PiperOrigin-RevId: 347035065 -- 5a035c0d9840b251967f9e7039fc6a4e01dd52f3 by Abseil Team : Restructure Cord::ChunkIterator for future ring buffer support. PiperOrigin-RevId: 346890054 GitOrigin-RevId: 0bfa836596a9c787a2f0bdc283011dd1f6810c6e Change-Id: I3a58e2a44cb4c6f2116c43e2a4ccbc319d3ccecf --- absl/numeric/bits.h | 177 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 177 insertions(+) create mode 100644 absl/numeric/bits.h (limited to 'absl/numeric/bits.h') diff --git a/absl/numeric/bits.h b/absl/numeric/bits.h new file mode 100644 index 00000000..52013ad4 --- /dev/null +++ b/absl/numeric/bits.h @@ -0,0 +1,177 @@ +// Copyright 2020 The Abseil Authors +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// ----------------------------------------------------------------------------- +// File: bits.h +// ----------------------------------------------------------------------------- +// +// This file contains implementations of C++20's bitwise math functions, as +// defined by: +// +// P0553R4: +// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0553r4.html +// P0556R3: +// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0556r3.html +// P1355R2: +// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1355r2.html +// P1956R1: +// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1956r1.pdf +// +// When using a standard library that implements these functions, we use the +// standard library's implementation. + +#ifndef ABSL_NUMERIC_BITS_H_ +#define ABSL_NUMERIC_BITS_H_ + +#include +#include +#include + +#if (defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L) || \ + (defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L) +#include +#endif + +#include "absl/base/attributes.h" +#include "absl/base/config.h" +#include "absl/numeric/internal/bits.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +#if !(defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L) +// rotating +template +ABSL_MUST_USE_RESULT constexpr + typename std::enable_if::value, T>::type + rotl(T x, int s) noexcept { + return numeric_internal::RotateLeft(x, s); +} + +template +ABSL_MUST_USE_RESULT constexpr + typename std::enable_if::value, T>::type + rotr(T x, int s) noexcept { + return numeric_internal::RotateRight(x, s); +} + +// Counting functions +// +// While these functions are typically constexpr, on some platforms, they may +// not be marked as constexpr due to constraints of the compiler/available +// intrinsics. +template +ABSL_INTERNAL_CONSTEXPR_CLZ inline + typename std::enable_if::value, int>::type + countl_zero(T x) noexcept { + return numeric_internal::CountLeadingZeroes(x); +} + +template +ABSL_INTERNAL_CONSTEXPR_CLZ inline + typename std::enable_if::value, int>::type + countl_one(T x) noexcept { + // Avoid integer promotion to a wider type + return countl_zero(static_cast(~x)); +} + +template +ABSL_INTERNAL_CONSTEXPR_CTZ inline + typename std::enable_if::value, int>::type + countr_zero(T x) noexcept { + return numeric_internal::CountTrailingZeroes(x); +} + +template +ABSL_INTERNAL_CONSTEXPR_CTZ inline + typename std::enable_if::value, int>::type + countr_one(T x) noexcept { + // Avoid integer promotion to a wider type + return countr_zero(static_cast(~x)); +} + +template +ABSL_INTERNAL_CONSTEXPR_POPCOUNT inline + typename std::enable_if::value, int>::type + popcount(T x) noexcept { + return numeric_internal::Popcount(x); +} +#else // defined(__cpp_lib_bitops) && __cpp_lib_bitops >= 201907L + +using std::countl_one; +using std::countl_zero; +using std::countr_one; +using std::countr_zero; +using std::popcount; +using std::rotl; +using std::rotr; + +#endif + +#if !(defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L) +// Returns: true if x is an integral power of two; false otherwise. +template +constexpr inline typename std::enable_if::value, bool>::type +has_single_bit(T x) noexcept { + return x != 0 && (x & (x - 1)) == 0; +} + +// Returns: If x == 0, 0; otherwise one plus the base-2 logarithm of x, with any +// fractional part discarded. +template +ABSL_INTERNAL_CONSTEXPR_CLZ inline + typename std::enable_if::value, T>::type + bit_width(T x) noexcept { + return std::numeric_limits::digits - countl_zero(x); +} + +// Returns: If x == 0, 0; otherwise the maximal value y such that +// has_single_bit(y) is true and y <= x. +template +ABSL_INTERNAL_CONSTEXPR_CLZ inline + typename std::enable_if::value, T>::type + bit_floor(T x) noexcept { + return x == 0 ? 0 : T{1} << (bit_width(x) - 1); +} + +// Returns: N, where N is the smallest power of 2 greater than or equal to x. +// +// Preconditions: N is representable as a value of type T. +template +ABSL_INTERNAL_CONSTEXPR_CLZ inline + typename std::enable_if::value, T>::type + bit_ceil(T x) { + // If T is narrower than unsigned, T{1} << bit_width will be promoted. We + // want to force it to wraparound so that bit_ceil of an invalid value are not + // core constant expressions. + // + // BitCeilNonPowerOf2 triggers an overflow in constexpr contexts if we would + // undergo promotion to unsigned but not fit the result into T without + // truncation. + return has_single_bit(x) ? T{1} << (bit_width(x) - 1) + : numeric_internal::BitCeilNonPowerOf2(x); +} +#else // defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L + +using std::bit_ceil; +using std::bit_floor; +using std::bit_width; +using std::has_single_bit; + +#endif + +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_NUMERIC_BITS_H_ -- cgit v1.2.3