Perl does its own "sprintf" formatting--it emulates the C function "sprintf", but it doesn't use it (except for floating- point numbers, and even then only the standard modifiers are allowed). As a result, any non-standard extensions in your local "sprintf" are not available from Perl.

And what's incorrect about that? Perl prefers the "nearest even round" operation, as I recall, but otherwise should work the same as your local sprintf.

-- Randal L. Schwartz, Perl hacker

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

It's incorrect because it claims that it does use local sptrinf() for floating point operators, not some internal emulation.

Or maybe I'm misreading the whole thing?

"What should it profit a man, if he should win a flame war, yet lose his cool?"

$ perl -v

This is perl, v5.8.8 built for x86_64-linux-gnu-thread-multi

$ perl -e 'printf "%.2f\n%.2f\n", 0.335, 1.335;'
0.34
1.33
[download]

and

C:\>perl -v

This is perl, v5.8.9 built for MSWin32-x86-multi-thread
(with 9 registered patches, see perl -V for more detail)

C:\>perl -e "printf qq{%.2f\n%.2f\n}, 0.335, 1.335;"
0.34
1.34
[download]

Am I missing something (as usual)?

Update:

Following ikegami's suggestion, I tried increasing the precision to 40 digits, and got:

$ perl -v

This is perl, v5.8.8 built for x86_64-linux-gnu-thread-multi

$ perl -e 'printf "%.40f\n%.40f\n", 0.335, 1.335;'
0.3350000000000000199840144432528177276254
1.3349999999999999644728632119949907064438

C:\>perl -v

This is perl, v5.8.9 built for MSWin32-x86-multi-thread
(with 9 registered patches, see perl -V for more detail)

C:\>perl -e "printf qq{%.40f\n%.40f\n}, 0.335, 1.335;"
0.3350000000000000200000000000000000000000
1.3350000000000000000000000000000000000000
[download]

It looks like this variation is just an artifact of 64-bit vs. 32-bit, emphasizing how you should never rely on precise results from rounding.

I think the main problem is that neither of those two numbers can be accurately represented by binary (IEEE) floating points.

For what it's worth, I get the same results as your linux test on my intel macbook, v5.8.9 built for darwin-2level and v5.8.8 built for darwin-thread-multi-2level.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

I bet perl -e'printf "%.40e\n", 0.335' gives 0.334999... on the system that rounded to 1.33. Let me know if not.