Fix issue https://github.com/yuin/gopher-lua/issues/214

bits.go

@@ -0,0 +1,46 @@
+// This is a port of the bits.go file from the dolthub/swiss repository.
+// The original source code is licensed under the Apache License, Version 2.0.
+// The original source code can be found at:
+// https://github.com/dolthub/swiss
+
+//go:build !amd64 || nosimd
+
+package lua
+
+import (
+	"math/bits"
+	"unsafe"
+)
+
+const (
+	groupSize       = 8
+	maxAvgGroupLoad = 7
+
+	loBits uint64 = 0x0101010101010101
+	hiBits uint64 = 0x8080808080808080
+)
+
+type bitset uint64
+
+func metaMatchH2(m *metadata, h h2) bitset {
+	// https://graphics.stanford.edu/~seander/bithacks.html##ValueInWord
+	return hasZeroByte(castUint64(m) ^ (loBits * uint64(h)))
+}
+
+func metaMatchEmpty(m *metadata) bitset {
+	return hasZeroByte(castUint64(m) ^ hiBits)
+}
+
+func nextMatch(b *bitset) uint32 {
+	s := uint32(bits.TrailingZeros64(uint64(*b)))
+	*b &= ^(1 << s) // clear bit |s|
+	return s >> 3   // div by 8
+}
+
+func hasZeroByte(x uint64) bitset {
+	return bitset(((x - loBits) & ^(x)) & hiBits)
+}
+
+func castUint64(m *metadata) uint64 {
+	return *(*uint64)((unsafe.Pointer)(m))
+}

bits_amd64.s

@@ -0,0 +1,19 @@
+// Code generated by command: go run asm.go -out match.s -stubs match_amd64.go. DO NOT EDIT.
+
+//go:build amd64
+
+#include "textflag.h"
+
+// func matchMetadata(metadata *[16]int8, hash int8) uint16
+// Requires: SSE2, SSSE3
+TEXT ·matchMetadata(SB), NOSPLIT, $0-18
+	MOVQ     metadata+0(FP), AX
+	MOVBLSX  hash+8(FP), CX
+	MOVD     CX, X0
+	PXOR     X1, X1
+	PSHUFB   X1, X0
+	MOVOU    (AX), X1
+	PCMPEQB  X1, X0
+	PMOVMSKB X0, AX
+	MOVW     AX, ret+16(FP)
+	RET