ext/bcmath - Fixed GH-17064: Correctly round rounding mode with zero edge case - #17065

This is not related to this bug, but it was changing a global value and was dangerous, so I fixed it incidentally.

The indentation added with foreach, making it difficult to see the change. I increased the test cases for scale 0 to test cases for scale 0, 5, and -5.

This line will break under UBSAN for the following code:

<?php
echo bcround("0.01", PHP_INT_MIN, RoundingMode::AwayFromZero);

This gives:

/run/media/niels/MoreData/php-8.4/ext/bcmath/libbcmath/src/round.c:74:13: runtime error: negation of -9223372036854775808 cannot be represented in type 'zend_long' (aka 'long'); cast to an unsigned type to negate this value to itself
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /run/media/niels/MoreData/php-8.4/ext/bcmath/libbcmath/src/round.c:74:13 

But since this is an extreme edge case that won't be hit in practice, I think it suffices here to just return 0 as a sentinel and throw an exception.

@nielsdos
Nice point, thanks!

The first argument is size_t, so how about this?

if (UNEXPECTED(precision == ZEND_LONG_MIN)) {
    *result = bc_new_num((size_t) ZEND_LONG_MAX + 2, 0);
}

Sure, it doesn't matter much as it'll fail to allocate that much memory anyway but it's a simple approach.

done!