ascii85 encoder in perl (take 2)

This time with line wrapping. Output matches that of encode85.c

Also, I used slurp mode in the previous one. That obviously chews a lot of memory for large files. I changed to just reading 4 byte chunks.

my ($in, $pos, $width) = (undef, 2, 72);
print "<~";
while (read(STDIN, $in, 4) > 0) {
    my (@a, @buf, $x, $i);

    @a = unpack("C4", $in);

    $x = $a[0] << 24 | $a[1] << 16 | $a[2] << 8 | $a[3];
    if (scalar(@a) == 4 && $x == 0) {
        $buf[0] = "z";                                      # '!!!!' -> 'z'
    } else {
        for $i (1 .. 5) {
            unshift @buf, chr(($x % 85) + 33);
            $x /= 85;
        }
        splice @buf, scalar(@a) + 1;                        # trim @buf
    }
    if (scalar(@buf) + $pos > $width) {                     # should we wrap?
        $pos = ($pos + scalar(@buf)) % ($width + 1);
        splice @buf, scalar(@buf) - $pos, 0, "\n";          # put a newline in
    } else {
        $pos = $pos + scalar(@buf);
    }
    print @buf;
}
print $pos <= $width - 2 ? "~>\n" : "\n~>\n";