feat: export GalMulSlice and GalMulSliceXor

Author: arajasek

mulslice.go

@@ -0,0 +1,40 @@
+package reedsolomon
+
+import "cmp"
+
+// LowLevel exposes low level functionality.
+type LowLevel struct {
+	o *options
+}
+
+// WithOptions resets the options to the default+provided options.
+// Options that don't apply to the called functions will be ignored.
+// This should not be called concurrent with other calls.
+func (l *LowLevel) WithOptions(opts ...Option) {
+	o := defaultOptions
+	for _, opt := range opts {
+		opt(&o)
+	}
+}
+
+func (l LowLevel) options() *options {
+	return cmp.Or(l.o, &defaultOptions)
+}
+
+// GalMulSlice multiplies the elements of in by c, writing the result to out: out[i] = c * in[i].
+// out must be at least as long as in.
+func (l LowLevel) GalMulSlice(c byte, in, out []byte) {
+	galMulSlice(c, in, out, l.options())
+}
+
+// GalMulSliceXor multiplies the elements of in by c, and adds the result to out: out[i] ^= c * in[i].
+// out must be at least as long as in.
+func (l LowLevel) GalMulSliceXor(c byte, in, out []byte) {
+	galMulSliceXor(c, in, out, l.options())
+}
+
+// Inv returns the multiplicative inverse of e in GF(2^8).
+// Should not be called with 0 (returns 0 in this case).
+func Inv(e byte) byte {
+	return invTable[e]
+}