internal/profile: optimize Parse performance

Author: pymq

src/internal/profile/proto.go

@@ -24,6 +24,7 @@ package profile
 import (
 	"errors"
 	"fmt"
+	"slices"
 )
 
 type buffer struct {
@@ -175,6 +176,16 @@ func le32(p []byte) uint32 {
 	return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
 }
 
+func peekNumVarints(data []byte) (numVarints int) {
+	for ; len(data) > 0; numVarints++ {
+		var err error
+		if _, data, err = decodeVarint(data); err != nil {
+			break
+		}
+	}
+	return numVarints
+}
+
 func decodeVarint(data []byte) (uint64, []byte, error) {
 	var i int
 	var u uint64
@@ -275,6 +286,9 @@ func decodeInt64(b *buffer, x *int64) error {
 func decodeInt64s(b *buffer, x *[]int64) error {
 	if b.typ == 2 {
 		// Packed encoding
+		dataLen := peekNumVarints(b.data)
+		*x = slices.Grow(*x, dataLen)
+
 		data := b.data
 		for len(data) > 0 {
 			var u uint64
@@ -305,8 +319,11 @@ func decodeUint64(b *buffer, x *uint64) error {
 
 func decodeUint64s(b *buffer, x *[]uint64) error {
 	if b.typ == 2 {
-		data := b.data
 		// Packed encoding
+		dataLen := peekNumVarints(b.data)
+		*x = slices.Grow(*x, dataLen)
+
+		data := b.data
 		for len(data) > 0 {
 			var u uint64
 			var err error