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Improve Battle Revolution checksum calc

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4.5 ms => 2.4 ms on my cpu (nearly 2x as fast), even better for lesser CPUs. Probably isn't worth parallelizing.
This commit is contained in:
Kurt 2026-01-08 19:50:46 -06:00
parent e2c09730b5
commit e9cb358c50
1 changed files with 46 additions and 5 deletions
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51
PKHeX.Core/Saves/SAV4BR.cs
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@ -1,6 +1,7 @@
using System;
using System.Buffers;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using static System.Buffers.Binary.BinaryPrimitives;
namespace PKHeX.Core;
@ -584,13 +585,53 @@ private static void WriteChecksums(Span<byte> span, Span<uint> checksums)
}
}
private static void ComputeChecksums(Span<byte> span, Span<uint> checksums)
private static void ComputeChecksums(ReadOnlySpan<byte> span, Span<uint> checksums)
{
for (int i = 0; i < span.Length; i += 2)
// Accumulate bit counts for each of the 16 bit positions across all u16 values.
// The save format is big-endian, so bit 0 of the u16 is the LSB of the *second* byte in each pair.
// We process as native ushort and fix up the mapping at the end based on endianness.
var u16 = MemoryMarshal.Cast<byte, ushort>(span);
uint b00 = 0, b01 = 0, b02 = 0, b03 = 0, b04 = 0, b05 = 0, b06 = 0, b07 = 0;
uint b08 = 0, b09 = 0, b10 = 0, b11 = 0, b12 = 0, b13 = 0, b14 = 0, b15 = 0;
foreach (var value in u16)
{
uint value = ReadUInt16BigEndian(span[i..]);
for (int c = 0; c < checksums.Length; c++)
checksums[c] += ((value >> c) & 1);
uint v = value;
b00 += (v ) & 1;
b01 += (v >> 1) & 1;
b02 += (v >> 2) & 1;
b03 += (v >> 3) & 1;
b04 += (v >> 4) & 1;
b05 += (v >> 5) & 1;
b06 += (v >> 6) & 1;
b07 += (v >> 7) & 1;
b08 += (v >> 8) & 1;
b09 += (v >> 9) & 1;
b10 += (v >> 10) & 1;
b11 += (v >> 11) & 1;
b12 += (v >> 12) & 1;
b13 += (v >> 13) & 1;
b14 += (v >> 14) & 1;
b15 += (v >> 15) & 1;
}
// On little-endian, native ushort has bytes swapped vs big-endian source.
// Bits 0-7 of native correspond to bits 8-15 of big-endian, and vice versa.
if (BitConverter.IsLittleEndian)
{
checksums[00] = b08; checksums[01] = b09; checksums[02] = b10; checksums[03] = b11;
checksums[04] = b12; checksums[05] = b13; checksums[06] = b14; checksums[07] = b15;
checksums[08] = b00; checksums[09] = b01; checksums[10] = b02; checksums[11] = b03;
checksums[12] = b04; checksums[13] = b05; checksums[14] = b06; checksums[15] = b07;
}
else
{
checksums[00] = b00; checksums[01] = b01; checksums[02] = b02; checksums[03] = b03;
checksums[04] = b04; checksums[05] = b05; checksums[06] = b06; checksums[07] = b07;
checksums[08] = b08; checksums[09] = b09; checksums[10] = b10; checksums[11] = b11;
checksums[12] = b12; checksums[13] = b13; checksums[14] = b14; checksums[15] = b15;
}
}
#endregion