From fbe52faf492619fd57a0dbe125c9f0c3bcceec19 Mon Sep 17 00:00:00 2001
From: greatroar <61184462+greatroar@users.noreply.github.com>
Date: Thu, 28 Jan 2021 14:23:24 +0100
Subject: [PATCH] lib/scanner: Allocate structure for final partial block
 (#7310)
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Benchmark results on Linux/amd64, using updated benchmark for old and
new:

name        old time/op    new time/op    delta
HashFile-8    88.6ms ± 1%    88.3ms ± 1%   -0.33%  (p=0.046 n=19+19)

name        old speed      new speed      delta
HashFile-8   201MB/s ± 1%   202MB/s ± 1%   +0.33%  (p=0.044 n=19+19)

name        old alloc/op   new alloc/op   delta
HashFile-8    59.4kB ± 0%    46.1kB ± 0%  -22.47%  (p=0.000 n=14+20)

name        old allocs/op  new allocs/op  delta
HashFile-8      29.0 ± 0%      27.0 ± 0%   -6.90%  (p=0.000 n=20+20)

Co-authored-by: greatroar <@>
---
 lib/scanner/blocks.go    | 8 ++++++--
 lib/scanner/walk_test.go | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/scanner/blocks.go b/lib/scanner/blocks.go
index f343b8ee2..d1a9ae0a5 100644
--- a/lib/scanner/blocks.go
+++ b/lib/scanner/blocks.go
@@ -30,7 +30,7 @@ func Blocks(ctx context.Context, r io.Reader, blocksize int, sizehint int64, cou
 	}
 
 	hf := sha256.New()
-	hashLength := hf.Size()
+	const hashLength = sha256.Size
 
 	var weakHf hash.Hash32 = noopHash{}
 	var multiHf io.Writer = hf
@@ -48,7 +48,11 @@ func Blocks(ctx context.Context, r io.Reader, blocksize int, sizehint int64, cou
 		// Allocate contiguous blocks for the BlockInfo structures and their
 		// hashes once and for all, and stick to the specified size.
 		r = io.LimitReader(r, sizehint)
-		numBlocks := int(sizehint / int64(blocksize))
+		numBlocks := sizehint / int64(blocksize)
+		remainder := sizehint % int64(blocksize)
+		if remainder != 0 {
+			numBlocks++
+		}
 		blocks = make([]protocol.BlockInfo, 0, numBlocks)
 		hashes = make([]byte, 0, hashLength*numBlocks)
 	}
diff --git a/lib/scanner/walk_test.go b/lib/scanner/walk_test.go
index dfa367462..06f313646 100644
--- a/lib/scanner/walk_test.go
+++ b/lib/scanner/walk_test.go
@@ -551,7 +551,7 @@ func (l testfileList) String() string {
 var initOnce sync.Once
 
 const (
-	testdataSize = 17 << 20
+	testdataSize = 17<<20 + 1
 	testdataName = "_random.data"
 )