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

8 files changed, 137 insertions, 39 deletions

diff --git a/lib/diskio/kmp.go b/lib/diskio/kmp.go
index 69a3a51..da19e81 100644
--- a/lib/diskio/kmp.go
+++ b/lib/diskio/kmp.go
@@ -9,12 +9,31 @@ import (
 	"io"
 )
 
+func mustGet[K ~int64, V any](seq Sequence[K, V], i K) V {
+	val, err := seq.Get(i)
+	if err != nil {
+		panic(err)
+	}
+	return val
+}
+
 // buildKMPTable takes the string 'substr', and returns a table such
 // that 'table[matchLen-1]' is the largest value 'val' for which 'val < matchLen' and
 // 'substr[:val] == substr[matchLen-val:matchLen]'.
-func buildKMPTable(substr []byte) []int {
-	table := make([]int, len(substr))
-	for j := range table {
+func buildKMPTable[K ~int64, V comparable](substr Sequence[K, V]) ([]K, error) {
+	var substrLen K
+	for {
+		if _, err := substr.Get(substrLen); err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return nil, err
+		}
+		substrLen++
+	}
+
+	table := make([]K, substrLen)
+	for j := K(0); j < substrLen; j++ {
 		if j == 0 {
 			// First entry must always be 0 (in order to
 			// satisfy 'val < matchLen').
@@ -22,62 +41,68 @@ func buildKMPTable(substr []byte) []int {
 		}
 		val := table[j-1]
 		// not a match; go back
-		for val > 0 && substr[j] != substr[val] {
+		for val > 0 && mustGet(substr, j) != mustGet(substr, val) {
 			val = table[val-1]
 		}
 		// is a match; go forward
-		if substr[val] == substr[j] {
+		if mustGet(substr, val) == mustGet(substr, j) {
 			val++
 		}
 		table[j] = val
 	}
-	return table
+	return table, nil
 }
 
-// FindAll returns the starting-position of all possibly-overlapping
-// occurances of 'substr' in the 'r' stream.
+// IndexAll returns the starting-position of all possibly-overlapping
+// occurances of 'substr' in the 'str' sequence.
 //
-// Will panic if len(substr)==0.
+// Will hop around in 'substr', but will only get the natural sequence
+// [0...) in order from 'str'.  When hopping around in 'substr' it
+// assumes that once it has gotten a given index without error, it can
+// continue to do so without error; errors appearing later will cause
+// panics.
+//
+// Will panic if the length of 'substr' is 0.
 //
 // Uses the Knuth-Morris-Pratt algorithm.
-func FindAll[A ~int64](r io.ByteReader, substr []byte) ([]A, error) {
-	if len(substr) == 0 {
-		panic(errors.New("diskio.FindAll: empty substring"))
+func IndexAll[K ~int64, V comparable](str, substr Sequence[K, V]) ([]K, error) {
+	table, err := buildKMPTable(substr)
+	if err != nil {
+		return nil, err
+	}
+	substrLen := K(len(table))
+	if substrLen == 0 {
+		panic(errors.New("diskio.IndexAll: empty substring"))
 	}
-	table := buildKMPTable(substr)
 
-	var matches []A
-	var curMatchBeg A
-	var curMatchLen int
+	var matches []K
+	var curMatchBeg K
+	var curMatchLen K
 
-	pos := A(-1) // if 'r' were a slice; define 'pos' such that 'chr=r[pos]'
-	for {
-		// I/O
-		var chr byte
-		chr, err := r.ReadByte()
+	for pos := K(0); ; pos++ {
+		chr, err := str.Get(pos)
 		if err != nil {
 			if errors.Is(err, io.EOF) {
 				err = nil
 			}
 			return matches, err
 		}
-		pos++
 
 		// Consider 'chr'
-		for curMatchLen > 0 && chr != substr[curMatchLen] { // shorten the match
+		for curMatchLen > 0 && chr != mustGet(substr, curMatchLen) { // shorten the match
 			overlap := table[curMatchLen-1]
-			curMatchBeg += A(curMatchLen - overlap)
+			curMatchBeg += curMatchLen - overlap
 			curMatchLen = overlap
 		}
-		if chr == substr[curMatchLen] { // lengthen the match
+		if chr == mustGet(substr, curMatchLen) { // lengthen the match
 			if curMatchLen == 0 {
 				curMatchBeg = pos
 			}
 			curMatchLen++
-			if curMatchLen == len(substr) {
+			if curMatchLen == substrLen {
 				matches = append(matches, curMatchBeg)
 				overlap := table[curMatchLen-1]
-				curMatchBeg += A(curMatchLen - overlap)
+				curMatchBeg += curMatchLen - overlap
 				curMatchLen = overlap
 			}
 		}
diff --git a/lib/diskio/kmp_test.go b/lib/diskio/kmp_test.go
index 836605a..51c7b5e 100644
--- a/lib/diskio/kmp_test.go
+++ b/lib/diskio/kmp_test.go
@@ -9,17 +9,19 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestBuildKMPTable(t *testing.T) {
-	substr := []byte("ababaa")
-	table := buildKMPTable(substr)
-	assert.Equal(t,
-		[]int{0, 0, 1, 2, 3, 1},
+	substr := SliceSequence[int64, byte]([]byte("ababaa"))
+	table, err := buildKMPTable[int64, byte](substr)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]int64{0, 0, 1, 2, 3, 1},
 		table)
 	for j, val := range table {
 		matchLen := j + 1
-		assert.Equalf(t, substr[:val], substr[matchLen-val:matchLen],
+		assert.Equalf(t, substr[:val], substr[matchLen-int(val):matchLen],
 			"for table[%d]=%d", j, val)
 	}
 }
@@ -27,17 +29,18 @@ func TestBuildKMPTable(t *testing.T) {
 func FuzzBuildKMPTable(f *testing.F) {
 	f.Add([]byte("ababaa"))
 	f.Fuzz(func(t *testing.T, substr []byte) {
-		table := buildKMPTable(substr)
-		assert.Equal(t, len(substr), len(table), "length")
+		table, err := buildKMPTable[int64, byte](SliceSequence[int64, byte](substr))
+		require.NoError(t, err)
+		require.Equal(t, len(substr), len(table), "length")
 		for j, val := range table {
 			matchLen := j + 1
-			assert.Equalf(t, substr[:val], substr[matchLen-val:matchLen],
+			assert.Equalf(t, substr[:val], substr[matchLen-int(val):matchLen],
 				"for table[%d]=%d", j, val)
 		}
 	})
 }
 
-func NaiveFindAll(str, substr []byte) []int64 {
+func NaiveIndexAll(str, substr []byte) []int64 {
 	var matches []int64
 	for i := range str {
 		if bytes.HasPrefix(str[i:], substr) {
@@ -47,15 +50,17 @@ func NaiveFindAll(str, substr []byte) []int64 {
 	return matches
 }
 
-func FuzzFindAll(f *testing.F) {
+func FuzzIndexAll(f *testing.F) {
 	f.Fuzz(func(t *testing.T, str, substr []byte) {
 		if len(substr) == 0 {
 			t.Skip()
 		}
 		t.Logf("str   =%q", str)
 		t.Logf("substr=%q", substr)
-		exp := NaiveFindAll(str, substr)
-		act, err := FindAll[int64](bytes.NewReader(str), substr)
+		exp := NaiveIndexAll(str, substr)
+		act, err := IndexAll[int64, byte](
+			&ByteReaderSequence[int64]{R: bytes.NewReader(str)},
+			SliceSequence[int64, byte](substr))
 		assert.NoError(t, err)
 		assert.Equal(t, exp, act)
 	})
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
+}
diff --git a/lib/diskio/testdata/fuzz/FuzzFindAll/593a5dd328ee86bac6820e3f98383aebadd2af3a22aa248546a228b08451c30d b/lib/diskio/testdata/fuzz/FuzzIndexAll/593a5dd328ee86bac6820e3f98383aebadd2af3a22aa248546a228b08451c30d
index 9d14adf..9d14adf 100644
--- a/lib/diskio/testdata/fuzz/FuzzFindAll/593a5dd328ee86bac6820e3f98383aebadd2af3a22aa248546a228b08451c30d
+++ b/lib/diskio/testdata/fuzz/FuzzIndexAll/593a5dd328ee86bac6820e3f98383aebadd2af3a22aa248546a228b08451c30d
diff --git a/lib/diskio/testdata/fuzz/FuzzFindAll/6bd9babbebf7eb78814e1f3425bfa6ccd6bfd42824a26e8cbd63b5117934e600 b/lib/diskio/testdata/fuzz/FuzzIndexAll/6bd9babbebf7eb78814e1f3425bfa6ccd6bfd42824a26e8cbd63b5117934e600
index 269f061..269f061 100644
--- a/lib/diskio/testdata/fuzz/FuzzFindAll/6bd9babbebf7eb78814e1f3425bfa6ccd6bfd42824a26e8cbd63b5117934e600
+++ b/lib/diskio/testdata/fuzz/FuzzIndexAll/6bd9babbebf7eb78814e1f3425bfa6ccd6bfd42824a26e8cbd63b5117934e600
diff --git a/lib/diskio/testdata/fuzz/FuzzFindAll/84ed65595ad05a58e293dbf423c1a816b697e2763a29d7c37aa476d6eef6fd60 b/lib/diskio/testdata/fuzz/FuzzIndexAll/84ed65595ad05a58e293dbf423c1a816b697e2763a29d7c37aa476d6eef6fd60
index b8f1562..b8f1562 100644
--- a/lib/diskio/testdata/fuzz/FuzzFindAll/84ed65595ad05a58e293dbf423c1a816b697e2763a29d7c37aa476d6eef6fd60
+++ b/lib/diskio/testdata/fuzz/FuzzIndexAll/84ed65595ad05a58e293dbf423c1a816b697e2763a29d7c37aa476d6eef6fd60
diff --git a/lib/diskio/testdata/fuzz/FuzzFindAll/9be40f71bc49b1b5c3b8e08d58d0f69cc22aefb12fd9b5931e49ff0e41953738 b/lib/diskio/testdata/fuzz/FuzzIndexAll/9be40f71bc49b1b5c3b8e08d58d0f69cc22aefb12fd9b5931e49ff0e41953738
index be67506..be67506 100644
--- a/lib/diskio/testdata/fuzz/FuzzFindAll/9be40f71bc49b1b5c3b8e08d58d0f69cc22aefb12fd9b5931e49ff0e41953738
+++ b/lib/diskio/testdata/fuzz/FuzzIndexAll/9be40f71bc49b1b5c3b8e08d58d0f69cc22aefb12fd9b5931e49ff0e41953738
diff --git a/lib/diskio/testdata/fuzz/FuzzFindAll/e43317ec61b0da9627d7b2fc0237d369082a6bf5dfe39e05c113b42ff6218d5d b/lib/diskio/testdata/fuzz/FuzzIndexAll/e43317ec61b0da9627d7b2fc0237d369082a6bf5dfe39e05c113b42ff6218d5d
index c3bfa37..c3bfa37 100644
--- a/lib/diskio/testdata/fuzz/FuzzFindAll/e43317ec61b0da9627d7b2fc0237d369082a6bf5dfe39e05c113b42ff6218d5d
+++ b/lib/diskio/testdata/fuzz/FuzzIndexAll/e43317ec61b0da9627d7b2fc0237d369082a6bf5dfe39e05c113b42ff6218d5d