Re-jigger the KMP search to be more independent of the underlying data types

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/diskio/seq.go b/lib/diskio/seq.go
new file mode 100644
index 0000000..3c5f4ae
--- /dev/null
+++ b/lib/diskio/seq.go
@@ -0,0 +1,68 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package diskio
+
+import (
+	"fmt"
+	"io"
+)
+
+// interface /////////////////////////////////////////////////////////
+
+type Sequence[K ~int64, V any] interface {
+	// Get the value at 'pos' in the sequence.  Positions start at
+	// 0 and increment naturally.  Return an error that is io.EOF
+	// if 'pos' is past the end of the sequence'.
+	Get(pos K) (V, error)
+}
+
+// implementation: slice /////////////////////////////////////////////
+
+type SliceSequence[K ~int64, V any] []V
+
+var _ Sequence[assertAddr, byte] = SliceSequence[assertAddr, byte]([]byte(nil))
+
+func (s SliceSequence[K, V]) Get(i K) (V, error) {
+	if i >= K(len(s)) {
+		var v V
+		return v, io.EOF
+	}
+	return s[int(i)], nil
+}
+
+// implementation: string ////////////////////////////////////////////
+
+type StringSequence[K ~int64] string
+
+var _ Sequence[assertAddr, byte] = StringSequence[assertAddr]("")
+
+func (s StringSequence[K]) Get(i K) (byte, error) {
+	if i >= K(len(s)) {
+		return 0, io.EOF
+	}
+	return s[int(i)], nil
+}
+
+// implementation: io.ByteReader /////////////////////////////////////
+
+type ByteReaderSequence[K ~int64] struct {
+	R   io.ByteReader
+	pos K
+}
+
+var _ Sequence[assertAddr, byte] = &ByteReaderSequence[assertAddr]{R: nil}
+
+func (s *ByteReaderSequence[K]) Get(i K) (byte, error) {
+	if i != s.pos {
+		return 0, fmt.Errorf("%T.Get(%v): can only call .Get(%v)",
+			s, i, s.pos)
+	}
+	chr, err := s.R.ReadByte()
+	if err != nil {
+		return chr, err
+	}
+	s.pos++
+	return chr, nil
+}