Returns the largest (closest to positive infinity) double value that is less than or equal to the argument and is equal to a mathematical integer. Special cases:
If the argument value is already equal to a mathematical integer, then the result is the same as the argument.
If the argument is NaN or an infinity or positive zero or negative zero, then the result is the same as the argument.
Parameters:
a - a value.
Returns:
the largest (closest to positive infinity) floating-point value that less than or equal to the argument and is equal to a mathematical integer.