git_unquote: perform modifications in-place

git_unquote: perform modifications in-place

This function doesn't have a lot of callers at the moment so
none of them are affected by this change.  But the plan is to
use this in our WWW code for things, so do it now before we
call it in more places.

Results from a Thinkpad X200 with a Core2Duo P8600 @ 2.4GHz:

Benchmark: timing 10 iterations of cp, ip...
        cp: 12.868 wallclock secs (12.86 usr +  0.00 sys = 12.86 CPU) @  0.78/s (n=10)
        ip: 10.9137 wallclock secs (10.91 usr +  0.00 sys = 10.91 CPU) @  0.92/s (n=10)

Note: I mainly care about unquoted performance because
that's the common case for the target audience of public-inbox.

Script used to get benchmark results against the Linux source tree:
==> bench_unquote.perl <==
use strict;
use warnings;
use Benchmark ':hireswallclock';
my $nr = 50;

my %GIT_ESC = (
	a => "\a",
	b => "\b",
	f => "\f",
	n => "\n",
	r => "\r",
	t => "\t",
	v => "\013",
);

sub git_unquote_ip ($) {
	return $_[0] unless ($_[0] =~ /\A"(.*)"\z/);
	$_[0] = $1;
	$_[0] =~ s/\\([abfnrtv])/$GIT_ESC{$1}/g;
	$_[0] =~ s/\\([0-7]{1,3})/chr(oct($1))/ge;
	$_[0];
}

sub git_unquote_cp ($) {
	my ($s) = @_;
	return $s unless ($s =~ /\A"(.*)"\z/);
	$s = $1;
	$s =~ s/\\([abfnrtv])/$GIT_ESC{$1}/g;
	$s =~ s/\\([0-7]{1,3})/chr(oct($1))/ge;
	$s;
}

chomp(my @files = `git -C ~/linux ls-tree --name-only -r v4.19.13`);
timethese(10, {
	cp => sub { for (0..$nr) { git_unquote_cp($_) for @files } },
	ip => sub { for (0..$nr) { git_unquote_ip($_) for @files } },
});