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#!/bin/sh

# vipatch -- edit unified diff

# This is a simple awk script that re-adjusts headers in
# a patch generated by diff -u, depending on the actual
# number of added/removed lines.

ep | awk -vname=${0##*/} '
/^@@ /		{ head = $0 "\n"; next }
head && /^---/	{ printpatch(); print; next }
head && /^\+/	{ plus++ }
head && /^-/	{ minus++ }
head && /^ /	{ same++ }
head		{ body = body $0 "\n"; next }
		{ print }
END		{ if (head) printpatch() }

function printpatch() {
	match(head, /,[0-9]+/)
	old = substr(head, RSTART+1, RLENGTH-1)
	new = old + plus - minus

	diff = old - same - minus
	if (diff != 0) {
		printf "%s: %d %s incorrectly %s\n", name, abs(diff),
			(abs(diff) > 1) ? "lines" : "line",
			(diff > 0) ? "removed" : "added" > "/dev/stderr"
		head = ""
		exit 1
	}

	match(head, /^@@ -[0-9]+,[0-9]+ \+[0-9]+,/)
	prefix = substr(head, RSTART, RLENGTH)

	match(head, / @@.*/)
	suffix = substr(head, RSTART, RLENGTH)

	printf "%s%d%s", prefix, new, suffix
	printf "%s", body

	head = ""; body = ""; plus = 0; minus = 0; same = 0
}

function abs(n) {
	return (n > 0) ? n : -n;
}
'