function logpmf( x, a, b ) {
	if (
		isnan( x ) ||
		isnan( a ) ||
		isnan( b ) ||
		!isInteger( a ) ||
		!isInteger( b ) ||
		a > b
	) {
		return NaN;
	}
	if ( x < a || x > b || !isInteger( x ) ) {
		return NINF;
	}
	return -ln( b - a + 1.0 );
}
Evaluates the natural logarithm of the probability mass function (PMF) 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 logPMF

@example
var y = logpmf( 2.0, 0, 4 );
// returns ~-1.609

@example
var y = logpmf( 5.0, 0, 4 );
// returns -Infinity

@example
var y = logpmf( 2, 0, 8 );
// returns ~-2.197

@example
var y = logpmf( NaN, 0.0, 1.0 );
// returns NaN

@example
var y = logpmf( 0.0, NaN, 1.0 );
// returns NaN

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

@example
var y = logpmf( 2.0, 3.0, 1.0 );
// returns NaN