From 686ecd83c04c9904de9457c7b14380cc2c04cff2 Mon Sep 17 00:00:00 2001
From: Nigel Tao <nigeltao@golang.org>
Date: Mon, 1 Sep 2014 10:02:52 +1000
Subject: [PATCH] image/png: make the CompressionLevel constants negative,
 reserving positive numbers to mean a numeric zlib compression level.

LGTM=bradfitz, ruiu
R=bradfitz, ruiu
CC=golang-codereviews, jeff.allen
https://golang.org/cl/138860043
---
 src/pkg/image/png/writer.go | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index b1a70c79d3..df23270ee9 100644
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -33,10 +33,13 @@ type encoder struct {
 type CompressionLevel int
 
 const (
-	DefaultCompression CompressionLevel = iota
-	NoCompression
-	BestSpeed
-	BestCompression
+	DefaultCompression CompressionLevel = 0
+	NoCompression      CompressionLevel = -1
+	BestSpeed          CompressionLevel = -2
+	BestCompression    CompressionLevel = -3
+
+	// Positive CompressionLevel values are reserved to mean a numeric zlib
+	// compression level, although that is not implemented yet.
 )
 
 // Big-endian.
-- 
2.48.1