Make the large file tests more robust/talkative as suggested by

Subject: Re: [ID 20001229.001] Not OK: perl v5.7.0 +DEVEL8221 on i686-linux 2.4.0-test13pre4-ac2 -2 (UNINSTALLED)
Message-ID: <m3snn7uzt6.fsf@ak-71.mind.de>

p4raw-id: //depot/perl@8258

1 files changed, 27 insertions, 4 deletions

diff --git a/t/op/lfs.t b/t/op/lfs.t
index e732adc798..e04e1a1dac 100644
--- a/t/op/lfs.t
+++ b/t/op/lfs.t
@@ -13,6 +13,10 @@ BEGIN {
 	}
 }
 
+use strict;
+our @s;
+our $fail;
+
 sub zap {
     close(BIG);
     unlink("big");
@@ -167,6 +171,20 @@ sub fail () {
     $fail++;
 }
 
+sub offset ($$) {
+    my ($offset_will_be, $offset_want) = @_;
+    my $offset_is = eval $offset_will_be;
+    unless ($offset_is == $offset_want) {
+        print "# bad offset $offset_is, want $offset_want\n";
+	if (unpack("L", pack("L", $offset_want)) == $offset_is) {
+	    my $offset_func = ($offset_will_be =~ /^(\w+)/);
+	    print "# 32-bit wraparound suspected in $offset_func() since\n";
+	    print "# $offset_want cast into 32 bits is $offset_is.\n";
+	}
+        fail;
+    }
+}
+
 print "1..17\n";
 
 my $fail = 0;
@@ -189,25 +207,28 @@ binmode BIG;
 fail unless seek(BIG, 4_500_000_000, $SEEK_SET);
 print "ok 5\n";
 
-fail unless tell(BIG) == 4_500_000_000;
+offset('tell(BIG)', 4_500_000_000);
 print "ok 6\n";
 
 fail unless seek(BIG, 1, $SEEK_CUR);
 print "ok 7\n";
 
-fail unless tell(BIG) == 4_500_000_001;
+# If you get 205_032_705 from here it means that
+# your tell() is returning 32-bit values since (I32)4_500_000_001
+# is exactly 205_032_705.
+offset('tell(BIG)', 4_500_000_001);
 print "ok 8\n";
 
 fail unless seek(BIG, -1, $SEEK_CUR);
 print "ok 9\n";
 
-fail unless tell(BIG) == 4_500_000_000;
+offset('tell(BIG)', 4_500_000_000);
 print "ok 10\n";
 
 fail unless seek(BIG, -3, $SEEK_END);
 print "ok 11\n";
 
-fail unless tell(BIG) == 5_000_000_000;
+offset('tell(BIG)', 5_000_000_000);
 print "ok 12\n";
 
 my $big;
@@ -219,6 +240,8 @@ fail unless $big eq "big";
 print "ok 14\n";
 
 # 705_032_704 = (I32)5_000_000_000
+# See that we don't have "big" in the 705_... spot:
+# that would mean that we have a wraparound.
 fail unless seek(BIG, 705_032_704, $SEEK_SET);
 print "ok 15\n";