From c546ea2ef7df1fd4069e167857eb2a409ad43c0c Mon Sep 17 00:00:00 2001
From: Derek Parker <parkerderek86@gmail.com>
Date: Mon, 14 Jul 2014 13:30:04 -0500
Subject: [PATCH] Reduce running time / allocations of frame parser

---
 dwarf/frame/frame_parser.go      | 23 ++++++++++-------------
 dwarf/frame/frame_parser_test.go | 11 +++++++++++
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/dwarf/frame/frame_parser.go b/dwarf/frame/frame_parser.go
index 4f3fdd23..e3e60d81 100644
--- a/dwarf/frame/frame_parser.go
+++ b/dwarf/frame/frame_parser.go
@@ -6,7 +6,6 @@ package frame
 import (
 	"bytes"
 	"encoding/binary"
-	"io"
 
 	"github.com/derekparker/dbg/dwarf/util"
 )
@@ -44,7 +43,7 @@ func cieEntry(data []byte) bool {
 func parseLength(ctx *parseContext) parsefunc {
 	var fn parsefunc
 
-	binary.Read(ctx.Buf, binary.LittleEndian, &ctx.Length)
+	ctx.Length = binary.LittleEndian.Uint32(ctx.Buf.Next(4))
 	cieid := ctx.Buf.Next(4)
 
 	if cieEntry(cieid) {
@@ -63,7 +62,7 @@ func parseLength(ctx *parseContext) parsefunc {
 }
 
 func parseInitialLocation(ctx *parseContext) parsefunc {
-	binary.Read(ctx.Buf, binary.LittleEndian, &ctx.Frame.AddressRange.begin)
+	ctx.Frame.AddressRange.begin = binary.LittleEndian.Uint64(ctx.Buf.Next(8))
 
 	ctx.Length -= 8
 
@@ -71,7 +70,7 @@ func parseInitialLocation(ctx *parseContext) parsefunc {
 }
 
 func parseAddressRange(ctx *parseContext) parsefunc {
-	binary.Read(ctx.Buf, binary.LittleEndian, &ctx.Frame.AddressRange.end)
+	ctx.Frame.AddressRange.end = binary.LittleEndian.Uint64(ctx.Buf.Next(8))
 
 	ctx.Length -= 8
 
@@ -82,17 +81,18 @@ func parseFrameInstructions(ctx *parseContext) parsefunc {
 	// The rest of this entry consists of the instructions
 	// so we can just grab all of the data from the buffer
 	// cursor to length.
-	var buf = make([]byte, ctx.Length)
-
-	io.ReadFull(ctx.Buf, buf)
-	ctx.Frame.Instructions = buf
+	ctx.Frame.Instructions = ctx.Buf.Next(int(ctx.Length))
 	ctx.Length = 0
 
 	return parseLength
 }
 
 func parseVersion(ctx *parseContext) parsefunc {
-	binary.Read(ctx.Buf, binary.LittleEndian, &ctx.Common.Version)
+	version, err := ctx.Buf.ReadByte()
+	if err != nil {
+		panic(err)
+	}
+	ctx.Common.Version = version
 	ctx.Length -= 1
 
 	return parseAugmentation
@@ -137,10 +137,7 @@ func parseInitialInstructions(ctx *parseContext) parsefunc {
 	// The rest of this entry consists of the instructions
 	// so we can just grab all of the data from the buffer
 	// cursor to length.
-	var buf = make([]byte, ctx.Length)
-
-	binary.Read(ctx.Buf, binary.LittleEndian, &buf)
-	ctx.Common.InitialInstructions = buf
+	ctx.Common.InitialInstructions = ctx.Buf.Next(int(ctx.Length))
 	ctx.Length = 0
 
 	return parseLength
diff --git a/dwarf/frame/frame_parser_test.go b/dwarf/frame/frame_parser_test.go
index d619ef45..c2d16acb 100644
--- a/dwarf/frame/frame_parser_test.go
+++ b/dwarf/frame/frame_parser_test.go
@@ -3,6 +3,7 @@ package frame_test
 import (
 	"testing"
 
+	"github.com/davecheney/profile"
 	"github.com/derekparker/dbg/dwarf/frame"
 )
 
@@ -38,3 +39,13 @@ func TestParse(t *testing.T) {
 	}
 
 }
+
+func BenchmarkParse(b *testing.B) {
+	defer profile.Start(profile.CPUProfile).Stop()
+	data := grabDebugFrameSection("../../_fixtures/testprog", nil)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		frame.Parse(data)
+	}
+}
-- 
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