cpp/numeric/math/floor

@1-3@ Computes the largest integer value not greater than.

Return value
If no errors occur, the largest integer value not greater than, that is $⌊num⌋$, is returned.

Error handling
Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),
 * The current rounding mode has no effect.
 * If is ±∞, it is returned, unmodified
 * If is ±0, it is returned, unmodified
 * If is NaN, NaN is returned