Fixed GH-12237: sprintf/printf no longer produces negative zero

[lacatoire]

Summary

When a negative floating-point value rounds to zero at the requested precision, sprintf/printf now outputs "0.00" instead of "-0.00".

// Before (8.4 and earlier)
sprintf('%.2f', -0.001);  // "-0.00"
sprintf('%.0f', -0.1);    // "-0"

// After
sprintf('%.2f', -0.001);  // "0.00"
sprintf('%.0f', -0.1);    // "0"

This aligns the behavior of sprintf()/printf() with number_format(), which already suppresses the negative sign for values that round to zero.

Fix

After php_conv_fp() formats the number, if is_negative is set, we check whether round(fabs(number) * 10^precision) / 10^precision == 0.0. If so, we clear the negative flag.

The check is only applied to %f/%F formats (for %e/%E, a non-zero value never formats as zero).

[alexandre-daubois]

This looks like a BC break, isn't it? Also, tests are failing

[ndossche]

This looks like a BC break, isn't it?

If this restores previous behaviour that was unintentionally changed, then it is a regression bugfix.

[alexandre-daubois]

Ah yes I missed that part, sorry!