Commit 61e9e82bdc

LemonBoy <thatlemon@gmail.com>
2020-09-13 21:12:21
std: Make the CRC32 calculation slightly faster
Speed up a little the slicing-by-8 code path by replacing the (load+shift+xor)*4 sequence with a single u32 load plus a xor. Before: ``` iterative: 1018 MiB/s [000000006c3b110d] small keys: 1075 MiB/s [0035bf3dcac00000] ``` After: ``` iterative: 1114 MiB/s [000000006c3b110d] small keys: 1324 MiB/s [0035bf3dcac00000] ```
master
1 parent 5e50d14
Changed files (1)
lib
std
hash
crc.zig
lib/std/hash/crc.zig
@@ -71,10 +71,7 @@ pub fn Crc32WithPoly(comptime poly: Polynomial) type {
                 const p = input[i .. i + 8];
 
                 // Unrolling this way gives ~50Mb/s increase
-                self.crc ^= (@as(u32, p[0]) << 0);
-                self.crc ^= (@as(u32, p[1]) << 8);
-                self.crc ^= (@as(u32, p[2]) << 16);
-                self.crc ^= (@as(u32, p[3]) << 24);
+                self.crc ^= std.mem.readIntLittle(u32, p[0..4]);
 
                 self.crc =
                     lookup_tables[0][p[7]] ^