misc/benchcmp: benchmark comparison script

I've been using this since April and posted it on the
mailing list, but it seems worth having in the repository.
Not sure about the location.

R=golang-dev, r, r
CC=golang-dev
https://golang.org/cl/5371100

misc/benchcmp

@@ -0,0 +1,66 @@
+#!/bin/sh
+# Copyright 2011 The Go Authors.  All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+case "$1" in
+-*)	
+	echo 'usage: benchcmp old.txt new.txt' >&2
+	echo >&2
+	echo 'Each input file should be gotest -bench output.' >&2
+	echo 'Benchcmp compares the first and last for each benchmark.' >&2
+	exit 2
+esac
+
+awk '
+BEGIN {
+	n = 0
+}
+
+$1 ~ /^Benchmark/ && $4 == "ns/op" {
+	if(old[$1]) {
+		if(!saw[$1]++) {
+			name[n++] = $1
+			if(length($1) > len)
+				len = length($1)
+		}
+		new[$1] = $3
+		if($6 == "MB/s")
+			newmb[$1] = $5
+	} else {
+		old[$1] = $3
+		if($6 = "MB/s")
+			oldmb[$1] = $5
+	}
+}
+
+END {
+	if(n == 0) {
+		print "benchcmp: no repeated benchmarks" >"/dev/stderr"
+		exit 1
+	}
+
+	printf("%-*s %12s %12s  %7s\n", len, "benchmark", "old ns/op", "new ns/op", "delta")
+
+	# print ns/op
+	for(i=0; i<n; i++) {
+		what = name[i]
+		printf("%-*s %12d %12d  %6s%%\n", len, what, old[what], new[what],
+			sprintf("%+.2f", 100*new[what]/old[what]-100))
+	}
+
+	# print mb/s
+	anymb = 0
+	for(i=0; i<n; i++) {
+		what = name[i]
+		if(!(what in newmb))
+			continue
+		if(anymb++ == 0)
+			printf("\n%-*s %12s %12s  %7s\n", len, "benchmark", "old MB/s", "new MB/s", "speedup")
+		printf("%-*s %12s %12s  %6sx\n", len, what,
+			sprintf("%.2f", oldmb[what]),
+			sprintf("%.2f", newmb[what]),
+			sprintf("%.2f", newmb[what]/oldmb[what]))
+	}
+}
+' "$@"