From 3d6c263446502ff72cf11bcd281529d7f2a512f7 Mon Sep 17 00:00:00 2001 From: Ben Clayton Date: Thu, 12 Jan 2023 18:23:28 +0000 Subject: [PATCH] tint/utils: Add Log2 and NextPowerOfTwo Shamelessly adapted from dawn's implementations. Change-Id: I77aff9bd1c852c14b0009295024973aa17c50d55 Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/116873 Kokoro: Kokoro Reviewed-by: Dan Sinclair Commit-Queue: Ben Clayton --- src/tint/utils/math.h | 51 +++++++++++++++++++++++++++-- src/tint/utils/math_test.cc | 64 +++++++++++++++++++++++++++++++++++++ 2 files changed, 113 insertions(+), 2 deletions(-) diff --git a/src/tint/utils/math.h b/src/tint/utils/math.h index 3d8874ab20..27dd232904 100644 --- a/src/tint/utils/math.h +++ b/src/tint/utils/math.h @@ -26,7 +26,7 @@ namespace tint::utils { /// @return `value` rounded to the next multiple of `alignment` /// @note `alignment` must be positive. An alignment of zero will cause a DBZ. template -inline T RoundUp(T alignment, T value) { +inline constexpr T RoundUp(T alignment, T value) { return ((value + alignment - 1) / alignment) * alignment; } @@ -34,10 +34,57 @@ inline T RoundUp(T alignment, T value) { /// @returns true if `value` is a power-of-two /// @note `value` must be positive if `T` is signed template -inline bool IsPowerOfTwo(T value) { +inline constexpr bool IsPowerOfTwo(T value) { return (value & (value - 1)) == 0; } +/// @param value the input value +/// @returns the base-2 logarithm of @p value +inline constexpr uint32_t Log2(uint64_t value) { +#if defined(__clang__) || defined(__GNUC__) + return 63 - static_cast(__builtin_clzll(value)); +#elif defined(_MSC_VER) && !defined(__clang__) && __cplusplus >= 202002L // MSVC and C++20+ + // note: std::is_constant_evaluated() added in C++20 + // required here as _BitScanReverse64 is not constexpr + if constexpr (!std::is_constant_evaluated()) { + // NOLINTNEXTLINE(runtime/int) + if constexpr (sizeof(unsigned long) == 8) { // 64-bit + // NOLINTNEXTLINE(runtime/int) + unsigned long first_bit_index = 0; + _BitScanReverse64(&first_bit_index, value); + return first_bit_index; + } else { // 32-bit + // NOLINTNEXTLINE(runtime/int) + unsigned long first_bit_index = 0; + if (_BitScanReverse(&first_bit_index, value >> 32)) { + return first_bit_index + 32; + } + _BitScanReverse(&first_bit_index, value & 0xffffffff); + return first_bit_index; + } + } +#endif + + // Non intrinsic (slow) path. Supports constexpr evaluation. + for (size_t clz = 0; clz < 64; clz++) { + size_t bit = 63 - clz; + if (value & (static_cast(1u) << bit)) { + return bit; + } + } + return 64; +} + +/// @param value the input value +/// @returns the next power of two number greater or equal to @p value +inline constexpr uint64_t NextPowerOfTwo(uint64_t value) { + if (value <= 1) { + return 1; + } else { + return static_cast(1) << (Log2(value - 1) + 1); + } +} + /// @param value the input value /// @returns the largest power of two that `value` is a multiple of template diff --git a/src/tint/utils/math_test.cc b/src/tint/utils/math_test.cc index 515c71823e..e8db5f7a5c 100644 --- a/src/tint/utils/math_test.cc +++ b/src/tint/utils/math_test.cc @@ -57,6 +57,70 @@ TEST(MathTests, IsPowerOfTwo) { EXPECT_EQ(IsPowerOfTwo(9), false); } +TEST(MathTests, Log2) { + EXPECT_EQ(Log2(1), 0u); + EXPECT_EQ(Log2(2), 1u); + EXPECT_EQ(Log2(3), 1u); + EXPECT_EQ(Log2(4), 2u); + EXPECT_EQ(Log2(5), 2u); + EXPECT_EQ(Log2(6), 2u); + EXPECT_EQ(Log2(7), 2u); + EXPECT_EQ(Log2(8), 3u); + EXPECT_EQ(Log2(9), 3u); + EXPECT_EQ(Log2(0x7fffffffu), 30u); + EXPECT_EQ(Log2(0x80000000u), 31u); + EXPECT_EQ(Log2(0x80000001u), 31u); + EXPECT_EQ(Log2(0x7fffffffffffffffu), 62u); + EXPECT_EQ(Log2(0x8000000000000000u), 63u); + + static_assert(Log2(1) == 0u); + static_assert(Log2(2) == 1u); + static_assert(Log2(3) == 1u); + static_assert(Log2(4) == 2u); + static_assert(Log2(5) == 2u); + static_assert(Log2(6) == 2u); + static_assert(Log2(7) == 2u); + static_assert(Log2(8) == 3u); + static_assert(Log2(9) == 3u); + static_assert(Log2(0x7fffffffu) == 30u); + static_assert(Log2(0x80000000u) == 31u); + static_assert(Log2(0x80000001u) == 31u); + static_assert(Log2(0x7fffffffffffffffu) == 62u); + static_assert(Log2(0x8000000000000000u) == 63u); +} + +TEST(MathTests, NextPowerOfTwo) { + EXPECT_EQ(NextPowerOfTwo(0), 1u); + EXPECT_EQ(NextPowerOfTwo(1), 1u); + EXPECT_EQ(NextPowerOfTwo(2), 2u); + EXPECT_EQ(NextPowerOfTwo(3), 4u); + EXPECT_EQ(NextPowerOfTwo(4), 4u); + EXPECT_EQ(NextPowerOfTwo(5), 8u); + EXPECT_EQ(NextPowerOfTwo(6), 8u); + EXPECT_EQ(NextPowerOfTwo(7), 8u); + EXPECT_EQ(NextPowerOfTwo(8), 8u); + EXPECT_EQ(NextPowerOfTwo(9), 16u); + EXPECT_EQ(NextPowerOfTwo(0x7fffffffu), 0x80000000u); + EXPECT_EQ(NextPowerOfTwo(0x80000000u), 0x80000000u); + EXPECT_EQ(NextPowerOfTwo(0x80000001u), 0x100000000u); + EXPECT_EQ(NextPowerOfTwo(0x7fffffffffffffffu), 0x8000000000000000u); + + static_assert(NextPowerOfTwo(0) == 1u); + static_assert(NextPowerOfTwo(1) == 1u); + static_assert(NextPowerOfTwo(2) == 2u); + static_assert(NextPowerOfTwo(3) == 4u); + static_assert(NextPowerOfTwo(4) == 4u); + static_assert(NextPowerOfTwo(5) == 8u); + static_assert(NextPowerOfTwo(6) == 8u); + static_assert(NextPowerOfTwo(7) == 8u); + static_assert(NextPowerOfTwo(8) == 8u); + static_assert(NextPowerOfTwo(9) == 16u); + static_assert(NextPowerOfTwo(0x7fffffffu) == 0x80000000u); + static_assert(NextPowerOfTwo(0x80000000u) == 0x80000000u); + static_assert(NextPowerOfTwo(0x80000001u) == 0x100000000u); + static_assert(NextPowerOfTwo(0x7fffffffffffffffu) == 0x8000000000000000u); +} + TEST(MathTests, MaxAlignOf) { EXPECT_EQ(MaxAlignOf(0u), 1u); EXPECT_EQ(MaxAlignOf(1u), 1u);