From 396d62533013a39b527db4b02195e816e36dbf9a Mon Sep 17 00:00:00 2001 From: Nigel Tao Date: Fri, 23 Aug 2019 16:28:23 +1000 Subject: [PATCH] compress/lzw: fix comment re high-code invariant MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The listed invariant, while technically true, was misleading, and the invariant can be tightened. We never actually get to (d.hi == d.overflow), due to the "d.hi--" line in the decoder.decode method. This is a comment-only commit, changing the comment to match the code. A follow-up commit could restore the comment, changing the code to match the original intented invariant. But the first step is to have the comment and the code say the same thing. Change-Id: Ifc9f78d5060454fc107af9be298026bf3043d400 Reviewed-on: https://go-review.googlesource.com/c/go/+/191358 Reviewed-by: Daniel Martí Reviewed-by: Bryan C. Mills Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot --- src/compress/lzw/reader.go | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/src/compress/lzw/reader.go b/src/compress/lzw/reader.go index 1be52d55e4f..912b7d3f40d 100644 --- a/src/compress/lzw/reader.go +++ b/src/compress/lzw/reader.go @@ -63,8 +63,7 @@ type decoder struct { // // last is the most recently seen code, or decoderInvalidCode. // - // An invariant is that - // (hi < overflow) || (hi == overflow && last == decoderInvalidCode) + // An invariant is that hi < overflow. clear, eof, hi, overflow, last uint16 // Each code c in [lo, hi] expands to two or more bytes. For c != hi: @@ -203,7 +202,7 @@ loop: if d.width == maxWidth { d.last = decoderInvalidCode // Undo the d.hi++ a few lines above, so that (1) we maintain - // the invariant that d.hi <= d.overflow, and (2) d.hi does not + // the invariant that d.hi < d.overflow, and (2) d.hi does not // eventually overflow a uint16. d.hi-- } else {