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New BitHelper APIs (#3362)
## PR Type What kind of change does this PR introduce? <!-- Please uncomment one or more that apply to this PR. --> <!-- - Bugfix --> - Feature <!-- - Code style update (formatting) --> <!-- - Refactoring (no functional changes, no api changes) --> <!-- - Build or CI related changes --> <!-- - Documentation content changes --> <!-- - Sample app changes --> <!-- - Other... Please describe: --> ## What is the new behavior? <!-- Describe how was this issue resolved or changed? --> This PR adds a few new APIs to the `BitHelper` class. Follow up from this original thread on Twitter: https://twitter.com/SergioPedri/status/1275556765363568641. These are the new APIs being included in this PR: ```csharp namespace Microsoft.Toolkit.HighPerformance.Helpers { public static class BitHelper { public static bool HasZeroByte(uint value); public static bool HasZeroByte(ulong value); public static bool HasByteEqualTo(uint value, byte target); public static bool HasByteEqualTo(ulong value, byte target); } } ``` ## PR Checklist Please check if your PR fulfills the following requirements: - [X] Tested code with current [supported SDKs](../readme.md#supported) - [ ] ~~Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->~~ - [ ] ~~Sample in sample app has been added / updated (for bug fixes / features)~~ - [ ] ~~Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)~~ - [X] Tests for the changes have been added (for bug fixes / features) (if applicable) - [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*) - [X] Contains **NO** breaking changes <!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. Please note that breaking changes are likely to be rejected. -->
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‎Microsoft.Toolkit.HighPerformance/Helpers/BitHelper.cs

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Original file line numberDiff line numberDiff line change
@@ -103,6 +103,68 @@ public static bool HasLookupFlag(uint table, int x, int min = 0)
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return valid;
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}
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/// <summary>
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/// Checks whether the given value has any bytes that are set to 0.
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/// That is, given a <see cref="uint"/> value, which has a total of 4 bytes,
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/// it checks whether any of those have all the bits set to 0.
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/// </summary>
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/// <param name="value">The input value to check.</param>
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/// <returns>Whether <paramref name="value"/> has any bytes set to 0.</returns>
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/// <remarks>
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/// This method contains no branches.
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/// For more background on this subject, see <see href="https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord"/>.
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/// </remarks>
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static bool HasZeroByte(uint value)
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{
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return ((value - 0x0101_0101u) & ~value & 0x8080_8080u) != 0;
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}
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/// <summary>
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/// Checks whether the given value has any bytes that are set to 0.
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/// This method mirrors <see cref="HasZeroByte(uint)"/>, but with <see cref="ulong"/> values.
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/// </summary>
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/// <param name="value">The input value to check.</param>
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/// <returns>Whether <paramref name="value"/> has any bytes set to 0.</returns>
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static bool HasZeroByte(ulong value)
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{
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return ((value - 0x0101_0101_0101_0101ul) & ~value & 0x8080_8080_8080_8080ul) != 0;
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}
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/// <summary>
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/// Checks whether a byte in the input <see cref="uint"/> value matches a target value.
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/// </summary>
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/// <param name="value">The input value to check.</param>
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/// <param name="target">The target byte to look for.</param>
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/// <returns>Whether <paramref name="value"/> has any bytes set to <paramref name="target"/>.</returns>
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/// <remarks>
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/// This method contains no branches.
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/// For more info, see <see href="https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord"/>.
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/// </remarks>
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static bool HasByteEqualTo(uint value, byte target)
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{
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return HasZeroByte(value ^ (0x0101_0101u * target));
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}
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/// <summary>
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/// Checks whether a byte in the input <see cref="uint"/> value matches a target value.
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/// This method mirrors <see cref="HasByteEqualTo(uint,byte)"/>, but with <see cref="ulong"/> values.
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/// </summary>
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/// <param name="value">The input value to check.</param>
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/// <param name="target">The target byte to look for.</param>
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/// <returns>Whether <paramref name="value"/> has any bytes set to <paramref name="target"/>.</returns>
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static bool HasByteEqualTo(ulong value, byte target)
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{
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return HasZeroByte(value ^ (0x0101_0101_0101_0101u * target));
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}
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/// <summary>
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/// Sets a bit to a specified value.
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/// </summary>

‎UnitTests/UnitTests.HighPerformance.Shared/Helpers/Test_BitHelper.cs

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@@ -77,6 +77,87 @@ public void Test_BitHelper_HasLookupFlag32_WithMin(int x, bool flag)
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Assert.AreEqual(flag, BitHelper.HasLookupFlag(mask, x, 40));
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}
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[TestCategory("BitHelper")]
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[TestMethod]
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[DataRow(0x0000_0000u, true)]
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[DataRow(0x0000_0001u, true)]
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[DataRow(0x0000_0011u, true)]
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[DataRow(0x0011_1111u, true)]
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[DataRow(0x1100_1111u, true)]
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[DataRow(0x1011_0011u, true)]
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[DataRow(0x1755_0055u, true)]
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[DataRow(0x0055_B255u, true)]
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[DataRow(0x1755_B200u, true)]
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[DataRow(0x1111_1111u, false)]
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[DataRow(0x1755_B255u, false)]
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[DataRow(0x1705_B255u, false)]
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[DataRow(0x1755_B055u, false)]
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public void Test_BitHelper_HasZeroByte_UInt32(uint x, bool result)
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{
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Assert.AreEqual(result, BitHelper.HasZeroByte(x));
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}
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[TestCategory("BitHelper")]
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[TestMethod]
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[DataRow(0x0000_0000_0000_0000ul, true)]
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[DataRow(0x0000_0000_0000_0001ul, true)]
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[DataRow(0x0000_0000_0000_0011ul, true)]
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[DataRow(0x0011_1111_1111_1111ul, true)]
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[DataRow(0x1111_0011_1111_1111ul, true)]
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[DataRow(0x7234_AB00_DEAD_BEEFul, true)]
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[DataRow(0x7234_A542_DEAD_BEEFul, false)]
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[DataRow(0x1111_1111_1111_1111ul, false)]
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[DataRow(0x7234_A542_DEAD_B0EFul, false)]
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[DataRow(0x7030_A040_0E0D_B0E0ul, false)]
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public void Test_BitHelper_HasZeroByte_UInt64(ulong x, bool result)
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{
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Assert.AreEqual(result, BitHelper.HasZeroByte(x));
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}
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[TestCategory("BitHelper")]
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[TestMethod]
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[DataRow(0x0000_0000u, 0x7B, false)]
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[DataRow(0x0000_0001u, 0x7B, false)]
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[DataRow(0x0000_1010u, 0x7B, false)]
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[DataRow(0x0111_7A00u, 0x7B, false)]
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[DataRow(0x0000_07B0u, 0x7B, false)]
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[DataRow(0x1111_1111u, 0x7B, false)]
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[DataRow(0x0000_FEFEu, 0xFF, false)]
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[DataRow(0xF00F_0FF0u, 0xFF, false)]
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[DataRow(0x0000_0000u, 0x00, true)]
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[DataRow(0x0000_007Bu, 0x7B, true)]
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[DataRow(0x0000_7B7Bu, 0x7B, true)]
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[DataRow(0x7B00_0110u, 0x7B, true)]
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[DataRow(0x00FF_0000u, 0xFF, true)]
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[DataRow(0xFFFF_FFFFu, 0xFF, true)]
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[DataRow(0x1515_1515u, 0x15, true)]
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public void Test_BitHelper_HasByteEqualTo_UInt32(uint x, int target, bool result)
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{
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Assert.AreEqual(result, BitHelper.HasByteEqualTo(x, unchecked((byte)target)));
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}
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[TestCategory("BitHelper")]
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[TestMethod]
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[DataRow(0x0000_0000_0000_0000u, 0x7B, false)]
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[DataRow(0x0000_0000_0000_0001u, 0x7B, false)]
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[DataRow(0x0000_0000_0000_1010u, 0x7B, false)]
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[DataRow(0x0111_0000_0000_7A00u, 0x7B, false)]
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[DataRow(0x0000_0000_0000_07B0u, 0x7B, false)]
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[DataRow(0x1111_1111_0000_0000u, 0x7B, false)]
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[DataRow(0x0000_FEFE_0000_0000u, 0xFF, false)]
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[DataRow(0xF00F_0000_0000_0FF0u, 0xFF, false)]
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[DataRow(0x0000_0000_0000_0000u, 0x00, true)]
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[DataRow(0x0000_0000_0000_007Bu, 0x7B, true)]
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[DataRow(0x0000_7B7B_0000_0000u, 0x7B, true)]
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[DataRow(0x7B00_0110_0000_0000u, 0x7B, true)]
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[DataRow(0x00FF_0000_0000_0000u, 0xFF, true)]
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[DataRow(0xFFFF_FFFF_FFFF_FFFFu, 0xFF, true)]
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[DataRow(0x1515_1515_1515_1515u, 0x15, true)]
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public void Test_BitHelper_HasByteEqualTo_UInt64(ulong x, int target, bool result)
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{
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Assert.AreEqual(result, BitHelper.HasByteEqualTo(x, unchecked((byte)target)));
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}
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[TestCategory("BitHelper")]
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[TestMethod]
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public void Test_BitHelper_SetFlag_UInt32()

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