1 files changed, 139 insertions, 0 deletions
diff --git a/src/internal/coverage/stringtab/stringtab.go b/src/internal/coverage/stringtab/stringtab.go
new file mode 100644
index 0000000..156c8ad
--- /dev/null
+++ b/src/internal/coverage/stringtab/stringtab.go
@@ -0,0 +1,139 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package stringtab
+
+import (
+	"fmt"
+	"internal/coverage/slicereader"
+	"internal/coverage/uleb128"
+	"io"
+)
+
+// This package implements string table writer and reader utilities,
+// for use in emitting and reading/decoding coverage meta-data and
+// counter-data files.
+
+// Writer implements a string table writing utility.
+type Writer struct {
+	stab   map[string]uint32
+	strs   []string
+	tmp    []byte
+	frozen bool
+}
+
+// InitWriter initializes a stringtab.Writer.
+func (stw *Writer) InitWriter() {
+	stw.stab = make(map[string]uint32)
+	stw.tmp = make([]byte, 64)
+}
+
+// Nentries returns the number of strings interned so far.
+func (stw *Writer) Nentries() uint32 {
+	return uint32(len(stw.strs))
+}
+
+// Lookup looks up string 's' in the writer's table, adding
+// a new entry if need be, and returning an index into the table.
+func (stw *Writer) Lookup(s string) uint32 {
+	if idx, ok := stw.stab[s]; ok {
+		return idx
+	}
+	if stw.frozen {
+		panic("internal error: string table previously frozen")
+	}
+	idx := uint32(len(stw.strs))
+	stw.stab[s] = idx
+	stw.strs = append(stw.strs, s)
+	return idx
+}
+
+// Size computes the memory in bytes needed for the serialized
+// version of a stringtab.Writer.
+func (stw *Writer) Size() uint32 {
+	rval := uint32(0)
+	stw.tmp = stw.tmp[:0]
+	stw.tmp = uleb128.AppendUleb128(stw.tmp, uint(len(stw.strs)))
+	rval += uint32(len(stw.tmp))
+	for _, s := range stw.strs {
+		stw.tmp = stw.tmp[:0]
+		slen := uint(len(s))
+		stw.tmp = uleb128.AppendUleb128(stw.tmp, slen)
+		rval += uint32(len(stw.tmp)) + uint32(slen)
+	}
+	return rval
+}
+
+// Write writes the string table in serialized form to the specified
+// io.Writer.
+func (stw *Writer) Write(w io.Writer) error {
+	wr128 := func(v uint) error {
+		stw.tmp = stw.tmp[:0]
+		stw.tmp = uleb128.AppendUleb128(stw.tmp, v)
+		if nw, err := w.Write(stw.tmp); err != nil {
+			return fmt.Errorf("writing string table: %v", err)
+		} else if nw != len(stw.tmp) {
+			return fmt.Errorf("short write emitting stringtab uleb")
+		}
+		return nil
+	}
+	if err := wr128(uint(len(stw.strs))); err != nil {
+		return err
+	}
+	for _, s := range stw.strs {
+		if err := wr128(uint(len(s))); err != nil {
+			return err
+		}
+		if nw, err := w.Write([]byte(s)); err != nil {
+			return fmt.Errorf("writing string table: %v", err)
+		} else if nw != len([]byte(s)) {
+			return fmt.Errorf("short write emitting stringtab")
+		}
+	}
+	return nil
+}
+
+// Freeze sends a signal to the writer that no more additions are
+// allowed, only lookups of existing strings (if a lookup triggers
+// addition, a panic will result). Useful as a mechanism for
+// "finalizing" a string table prior to writing it out.
+func (stw *Writer) Freeze() {
+	stw.frozen = true
+}
+
+// Reader is a helper for reading a string table previously
+// serialized by a Writer.Write call.
+type Reader struct {
+	r    *slicereader.Reader
+	strs []string
+}
+
+// NewReader creates a stringtab.Reader to read the contents
+// of a string table from 'r'.
+func NewReader(r *slicereader.Reader) *Reader {
+	str := &Reader{
+		r: r,
+	}
+	return str
+}
+
+// Read reads/decodes a string table using the reader provided.
+func (str *Reader) Read() {
+	numEntries := int(str.r.ReadULEB128())
+	str.strs = make([]string, 0, numEntries)
+	for idx := 0; idx < numEntries; idx++ {
+		slen := str.r.ReadULEB128()
+		str.strs = append(str.strs, str.r.ReadString(int64(slen)))
+	}
+}
+
+// Entries returns the number of decoded entries in a string table.
+func (str *Reader) Entries() int {
+	return len(str.strs)
+}
+
+// Get returns string 'idx' within the string table.
+func (str *Reader) Get(idx uint32) string {
+	return str.strs[idx]
+}