diff --git a/src/ImageSharp/Common/Helpers/Numerics.cs b/src/ImageSharp/Common/Helpers/Numerics.cs index e8ba6dde61..6bf06150b9 100644 --- a/src/ImageSharp/Common/Helpers/Numerics.cs +++ b/src/ImageSharp/Common/Helpers/Numerics.cs @@ -23,6 +23,28 @@ namespace SixLabors.ImageSharp private const int ShuffleAlphaControl = 0b_11_11_11_11; #endif +#if !SUPPORTS_BITOPERATIONS + /// + /// Gets the counts the number of bits needed to hold an integer. + /// + private static ReadOnlySpan BitCountLut => new byte[] + { + 0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, + 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, + 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, + 8, 8, 8, + }; +#endif + /// /// Determine the Greatest CommonDivisor (GCD) of two numbers. /// @@ -756,7 +778,7 @@ namespace SixLabors.ImageSharp /// widening them to 32-bit integers and performing four additions. /// /// - /// byte(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16) + /// byte(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16) /// is widened and added onto as such: /// /// accumulator += i32(1, 2, 3, 4); @@ -834,8 +856,17 @@ namespace SixLabors.ImageSharp [MethodImpl(MethodImplOptions.AggressiveInlining)] public static int MinimumBitsToStore(uint number) { +#if !SUPPORTS_BITOPERATIONS + if (number < 0x100) + { + return BitCountLut[(int)number]; + } + + return 8 + BitCountLut[(int)number >> 8]; +#else const int bitInUnsignedInteger = sizeof(uint) * 8; return bitInUnsignedInteger - BitOperations.LeadingZeroCount(number); +#endif } } }