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| author | Nigel Tao <nigeltao@golang.org> | 2019-09-12 17:56:57 +1000 |
|---|---|---|
| committer | Nigel Tao <nigeltao@golang.org> | 2019-09-14 02:23:31 +0000 |
| commit | 4e215554aa0e76e534327b9e6721971b9e82c113 (patch) | |
| tree | 342b0e2056220935c2c8ae423a4a9817ff9bce5d /src/compress | |
| parent | 8cc57c0ccc882a06352e6ad73cb7c281d34be3ef (diff) | |
| download | go-4e215554aa0e76e534327b9e6721971b9e82c113.tar.gz go-4e215554aa0e76e534327b9e6721971b9e82c113.zip | |
compress/lzw: clarify code invariants
This follows on from https://go-review.googlesource.com/c/go/+/191358
which was submitted as a comment-only change.
Benchmarks don't show any significant change:
compress/lzw
name old speed new speed delta
Decoder/1e4-56 92.8MB/s ± 1% 92.7MB/s ± 1% ~ (p=1.000 n=5+5)
Decoder/1e5-56 100MB/s ± 1% 100MB/s ± 1% ~ (p=0.746 n=5+5)
Decoder/1e6-56 101MB/s ± 1% 101MB/s ± 1% ~ (p=0.381 n=5+5)
image/gif
name old speed new speed delta
Decode-56 63.2MB/s ± 1% 63.2MB/s ± 1% ~ (p=0.690 n=5+5)
Change-Id: Ic36b5410cb06ca258da32e40da1f1ff6c44cff86
Reviewed-on: https://go-review.googlesource.com/c/go/+/194938
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src/compress')
| -rw-r--r-- | src/compress/lzw/reader.go | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/src/compress/lzw/reader.go b/src/compress/lzw/reader.go index 912b7d3f40..f08021190c 100644 --- a/src/compress/lzw/reader.go +++ b/src/compress/lzw/reader.go @@ -199,6 +199,9 @@ loop: } d.last, d.hi = code, d.hi+1 if d.hi >= d.overflow { + if d.hi > d.overflow { + panic("unreachable") + } if d.width == maxWidth { d.last = decoderInvalidCode // Undo the d.hi++ a few lines above, so that (1) we maintain @@ -207,7 +210,7 @@ loop: d.hi-- } else { d.width++ - d.overflow <<= 1 + d.overflow = 1 << d.width } } if d.o >= flushBuffer { |