From 17ea4f7fdd2b73bc32e855d4670bbeacdda5c713 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Sat, 23 Sep 2017 15:28:13 +1000
Subject: [PATCH] Performance optimizations to calculating bytes left in
 Torrent

Was generating significant overhead in cmd/torrent
---
 metainfo/info.go |  3 ---
 piece.go         | 10 +++++-----
 torrent.go       | 23 +++++++++++------------
 3 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/metainfo/info.go b/metainfo/info.go
index 7fbc88e9..a7e23a7f 100644
--- a/metainfo/info.go
+++ b/metainfo/info.go
@@ -126,9 +126,6 @@ func (info *Info) TotalLength() (ret int64) {
 }
 
 func (info *Info) NumPieces() int {
-	if len(info.Pieces)%20 != 0 {
-		panic(len(info.Pieces))
-	}
 	return len(info.Pieces) / 20
 }
 
diff --git a/piece.go b/piece.go
index 7a0c2f17..e09e00c8 100644
--- a/piece.go
+++ b/piece.go
@@ -128,11 +128,11 @@ func (p *Piece) chunkIndexSpec(chunk int) chunkSpec {
 }
 
 func (p *Piece) numDirtyBytes() (ret pp.Integer) {
-	defer func() {
-		if ret > p.length() {
-			panic("too many dirty bytes")
-		}
-	}()
+	// defer func() {
+	// 	if ret > p.length() {
+	// 		panic("too many dirty bytes")
+	// 	}
+	// }()
 	numRegularDirtyChunks := p.numDirtyChunks()
 	if p.chunkIndexDirty(p.numChunks() - 1) {
 		numRegularDirtyChunks--
diff --git a/torrent.go b/torrent.go
index 84691af6..3374778b 100644
--- a/torrent.go
+++ b/torrent.go
@@ -558,9 +558,11 @@ func (t *Torrent) bytesMissingLocked() int64 {
 }
 
 func (t *Torrent) bytesLeft() (left int64) {
-	for i := 0; i < t.numPieces(); i++ {
-		left += int64(t.pieces[i].bytesLeft())
-	}
+	bitmap.Flip(t.completedPieces, 0, t.numPieces()).IterTyped(func(piece int) bool {
+		p := t.pieces[piece]
+		left += int64(p.length() - p.numDirtyBytes())
+		return true
+	})
 	return
 }
 
@@ -658,17 +660,14 @@ type Peer struct {
 	SupportsEncryption bool
 }
 
-func (t *Torrent) pieceLength(piece int) (len_ pp.Integer) {
-	if piece < 0 || piece >= t.info.NumPieces() {
-		return
-	}
+func (t *Torrent) pieceLength(piece int) pp.Integer {
 	if piece == t.numPieces()-1 {
-		len_ = pp.Integer(t.length % t.info.PieceLength)
+		ret := pp.Integer(t.length % t.info.PieceLength)
+		if ret != 0 {
+			return ret
+		}
 	}
-	if len_ == 0 {
-		len_ = pp.Integer(t.info.PieceLength)
-	}
-	return
+	return pp.Integer(t.info.PieceLength)
 }
 
 func (t *Torrent) hashPiece(piece int) (ret metainfo.Hash) {