stat times decimals are off

[jdv]

The Problem

Decimal "stat" time values have mangled decimal portion.

Expected Behavior

The decimal portion to be exactly what the stat command kicks back.

Actual Behavior

The decimal portion is not exactly what the stat command kicks back.

Steps to Reproduce

jdv@jdv-lap:~$ cat test.raku

use nqp;

my $p = 'foo.txt'.IO;

qqx{touch $p.path()} unless $p.e;

qqx{stat $p.path()}.lines.grep(/^Mod/).say;

$p.modified.raku.say;

my $s := nqp::dispatch("boot-syscall", "file-stat", "foo.txt", 0);
my $m = nqp::dispatch(
"boot-syscall", "stat-time", $s, nqp::const::STAT_MODIFYTIME);
$m.raku.say;

jdv@jdv-lap:$ raku test.raku
(Modify: 2023-10-15 10:56:04.952796960 -0400)
Instant.from-posix(1697381764.952796928)
1697381764.952797e0
jdv@jdv-lap:$

Environment

• Operating system: debian 11
• Compiler version (rakudo -v or raku -v): v2023.08-277-g9866e7a1f

[MasterDuke17]

I believe this is "just" a num/float vs int problem (i.e., a difference in representation of the same underlying data, not incorrect data in the rakudo/moarvm case). "stat-time" returns a num (https://github.com/MoarVM/MoarVM/blob/main/src/disp/syscall.c#L1377) and I assume the stat command is printing the actual integer nanoseconds. Currently .modified() returns Instant.from-posix(nqp::dispatch("boot-syscall", "stat-time", $stat, nqp::const::STAT_MODIFYTIME)) (https://github.com/rakudo/rakudo/blob/main/src/core.c/IO/Path.rakumod#L964), but I wonder if instead it could do Instant.from-posix-nanos(nqp::dispatch("boot-syscall", "stat-time-int", $stat, nqp::const::STAT_MODIFYTIME)) (where stat-time-int is a new syscall that returns the seconds+nanoseconds, but as an int64 instead of a num)?

[MasterDuke17]

A quick test confirms it.

[dan@alexandria perl6]$ re 'use nqp; my $stat := nqp::dispatch("boot-syscall", "file-stat", "words.txt", 0); say "num: " ~ "words.txt".IO.modified; say "int: " ~ Instant.from-posix-nanos(nqp::dispatch("boot-syscall", "stat-time-nanos", $stat, nqp::const::STAT_MODIFYTIME));'
num: Instant:1490550860.46225894
int: Instant:1490550823.462259075
[dan@alexandria perl6]$ stat words.txt | grep Modify
Modify: 2017-03-26 13:53:43.462259075 -0400
[dan@alexandria perl6]$

It's also quite a bit faster. Running Instant.from-posix(nqp::dispatch("boot-syscall", "stat-time", $stat, nqp::const::STAT_MODIFYTIME)) 100k times takes ~0.093s, but running Instant.from-posix-nanos(nqp::dispatch("boot-syscall", "stat-time-nanos", $stat, nqp::const::STAT_MODIFYTIME)) 100k times takes only ~0.029s.