Description:
------------
printf does not properly format uppercase floats.

This is in the master branch and goes as far back as 5.6.40, but I didn't trace back any further.

The problem code is here:
https://github.com/php/php-src/blob/master/main/spprintf.c#L639

It only pays attention to a lower case 'f'

WARNING - FIXING this could cause unsuspected results as this bug has been present as far back as 5.6.40 at least (the furthest back I looked).

Specifically the code in microtime calls into the printf function (eventually), and this will change the output of microtime() to be locale-specific.

https://github.com/php/php-src/blob/master/ext/standard/microtime.c#L81

This is not necessarily a bad thing, but there are perhaps libraries that expect the buggy behavior at this point (e.g. one that I presently maintain: https://github.com/mmucklo/DtcQueueBundle/blob/5.0.0/Util/Util.php#L104-L105)

I'm not suggesting that it should not get fixed, but just to be cautious maybe where in the release cycle such a patch should go.

As a reference (couldn't instantly find a C version, but this CPP version seems accurate):
http://www.cplusplus.com/reference/cstdio/printf/

Also this Stackoverflow seems to clarify things. Pay particular attention to the second answer (about nan and inf capitalization), as I think PHP may do that wrong as well, although I didn't test it, but just looking at the code in spprintf.c, I don't see any specific logic to handle that case.

https://stackoverflow.com/questions/34706228/difference-between-upper-and-lower-case-double-float-type-specifiers-in-c



Test script:
---------------
<?php
// NOTE your system needs to have this locale loaded first
//  On ubuntu 19 which I'm using (via docker) do the following
//  from the shell prompt (if you are not root, become root, or prefix with sudo):
//
//  locale-gen de_DE
//  locale-gen de_DE.UTF-8
//  dpkg-reconfigure locales
//
//  # you may also need the locales package installed (apt install locales).
//

$loc_de = setlocale(LC_ALL, 'de_DE.UTF-8', 'de_DE', 'de', 'ge');

printf("%0.8f\n", 0.12345);
printf("%0.8F\n", 0.12335);

// One should show the comma, the other won't


/**

Here is some C code to reproduce the expected result

#include <stdio.h>
#include <locale.h>

int main(int argc, char**argv) {
	setlocale(LC_ALL, "de_DE.UTF-8");
	printf("%.8f\n", 0.12345);
	printf("%.8F\n", 0.12335);
	return 0;
}

*/

Expected result:
----------------
0,12345000
0,12335000


Actual result:
--------------
0,12345000
0.12335000