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Improve DynamicPackedIntArray.resize using a bit-interleaving algorithm, instead of fetching and putting the values one by one.

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fixes #322 (SIMD would be even faster, but at 0.05% of the total runtime, it doesn't make sense to go that far)
This commit is contained in:
IntegratedQuantum 2025-03-09 12:00:31 +01:00
parent 435d22083d
commit b5df364ab2
1 changed files with 22 additions and 6 deletions
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28
src/utils.zig
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@ -1334,13 +1334,29 @@ pub fn DynamicPackedIntArray(size: comptime_int) type { // MARK: DynamicPackedIn
self.* = .{};
}
pub fn resize(self: *Self, allocator: main.utils.NeverFailingAllocator, newBitSize: u5) void {
std.debug.assert(newBitSize == 0 or newBitSize & newBitSize - 1 == 0); // Must be a power of 2
if(newBitSize == self.bitSize) return;
inline fn bitInterleave(bits: comptime_int, source: u32) u32 {
var result = source;
if(bits <= 8) result = (result ^ (result << 8)) & 0x00ff00ff;
if(bits <= 4) result = (result ^ (result << 4)) & 0x0f0f0f0f;
if(bits <= 2) result = (result ^ (result << 2)) & 0x33333333;
if(bits <= 1) result = (result ^ (result << 1)) & 0x55555555;
return result;
}
pub fn resizeOnce(self: *Self, allocator: main.utils.NeverFailingAllocator) void {
const newBitSize = if(self.bitSize != 0) self.bitSize*2 else 1;
var newSelf = Self.initCapacity(allocator, newBitSize);
for(0..size) |i| {
newSelf.setValue(i, self.getValue(i));
switch(self.bitSize) {
0 => @memset(newSelf.data, 0),
inline 1, 2, 4, 8 => |bits| {
for(0..self.data.len) |i| {
const oldVal = self.data[i];
newSelf.data[2*i] = bitInterleave(bits, oldVal & 0xffff);
newSelf.data[2*i + 1] = bitInterleave(bits, oldVal >> 16);
}
},
else => unreachable,
}
allocator.free(self.data);
self.* = newSelf;
@ -1464,7 +1480,7 @@ pub fn PaletteCompressedRegion(T: type, size: comptime_int) type { // MARK: Pale
}
if(paletteIndex == self.paletteLength) {
if(self.paletteLength == self.palette.len) {
self.data.resize(main.globalAllocator, getTargetBitSize(self.paletteLength + 1));
self.data.resizeOnce(main.globalAllocator);
self.palette = main.globalAllocator.realloc(self.palette, @as(usize, 1) << self.data.bitSize);
const oldLen = self.paletteOccupancy.len;
self.paletteOccupancy = main.globalAllocator.realloc(self.paletteOccupancy, @as(usize, 1) << self.data.bitSize);