Re: [PATCH] p3400: stop using tac(1)

[Jeff King <peff@peff.net>]

On Tue, Oct 05, 2021 at 08:45:38PM +0200, René Scharfe wrote:

> Am 04.10.21 um 10:31 schrieb Jeff King:
> > On Sat, Oct 02, 2021 at 07:44:14PM +0200, René Scharfe wrote:
> >
> >> b3dfeebb92 (rebase: avoid computing unnecessary patch IDs, 2016-07-29)
> >> added a perf test that calls tac(1) from GNU core utilities.  Support
> >> systems without it by reversing the generated list using sort -nr
> >> instead.  sort(1) with options -n and -r is already used in other tests.
> >
> > Cute fix. With regular seq(1), this whole thing can become:
> >
> >   seq 1000 -1 1
> >
> > without the extra process, but our test_seq doesn't understand non-1
> > increments (nor comparisons besides -le). It wouldn't be that hard to
> > teach it, but given that this is the first time we've wanted it, it may
> > not be worth the effort.
> 
> Right.  The original also allows "seq 1000 1", by the way.  Not sure we
> need that either.

I'm not sure what you mean by "original" here. "seq 1000 1" produces no
output for me (nor does it work with test_seq).

> But when you say "without the extra process", I think:

I meant without the extra tac/sort process.

> test_seq () {
> 	set_step='END {step = first < last ? 1 : -1}'
> 	loop='END {for (; first <= last && step > 0 || first >= last && step < 0; first += step) print first}'
> 	case $# in
> 	1)      awk -v first=1    -v last="$1"    "$set_step $loop" ;;
> 	2)      awk -v first="$1" -v last="$2"    "$set_step $loop" ;;
> 	3)      awk -v first="$1" -v last="$3" -v step="$2" "$loop" ;;
> 	*)      BUG "not 1, 2, or 3 parameters to test_seq" ;;
> 	esac </dev/null
> }

Right, that works. It does introduce an extra awk process per
invocation, though I doubt that really matters all that much. The diff I
showed in my earlier response works totally in shell, like the current
test_seq().

-Peff