function logcdf( x, a, b ) {
	if (
		isnan( x ) ||
		isnan( a ) ||
		isnan( b ) ||
		!isInteger( a ) ||
		!isInteger( b ) ||
		a > b
	) {
		return NaN;
	}
	if ( x < a ) {
		return NINF;
	}
	if ( x >= b ) {
		return 0.0;
	}
	return ln( floor( x ) - a + 1.0 ) - ln( b - a + 1.0 );
}
Evaluates the natural logarithm of the cumulative distribution function (CDF) for a discrete uniform distribution with minimum support `a` and maximum support `b` at a value `x`.

@param {number} x - input value
@param {integer} a - minimum support
@param {integer} b - maximum support
@returns {number} evaluated logCDF

@example
var y = logcdf( 9.0, 0, 10 );
// returns ~-0.095

@example
var y = logcdf( 0.5, 0, 2 );
// returns ~-1.099

@example
var y = logcdf( +Infinity, 2, 4 );
// returns 0.0

@example
var y = logcdf( -Infinity, 2, 4 );
// returns -Infinity

@example
var y = logcdf( NaN, 0, 1 );
// returns NaN

@example
var y = logcdf( 0.0, NaN, 1 );
// returns NaN

@example
var y = logcdf( 0.0, 0, NaN );
// returns NaN

@example
var y = logcdf( 2.0, 1, 0 );
// returns NaN