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 <noreply+kokoro@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/utils/math.h b/src/tint/utils/math.h
index 3d8874a..27dd232 100644
--- a/src/tint/utils/math.h
+++ b/src/tint/utils/math.h
@@ -26,7 +26,7 @@
/// @return `value` rounded to the next multiple of `alignment`
/// @note `alignment` must be positive. An alignment of zero will cause a DBZ.
template <typename T>
-inline T RoundUp(T alignment, T value) {
+inline constexpr T RoundUp(T alignment, T value) {
return ((value + alignment - 1) / alignment) * alignment;
}
@@ -34,11 +34,58 @@
/// @returns true if `value` is a power-of-two
/// @note `value` must be positive if `T` is signed
template <typename T>
-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<uint32_t>(__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<size_t>(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<uint64_t>(1) << (Log2(value - 1) + 1);
+ }
+}
+
+/// @param value the input value
/// @returns the largest power of two that `value` is a multiple of
template <typename T>
inline std::enable_if_t<std::is_unsigned<T>::value, T> MaxAlignOf(T value) {
diff --git a/src/tint/utils/math_test.cc b/src/tint/utils/math_test.cc
index 515c718..e8db5f7 100644
--- a/src/tint/utils/math_test.cc
+++ b/src/tint/utils/math_test.cc
@@ -57,6 +57,70 @@
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);
