function accumulator( x, i ) {
		var sgn;
		var v;
		var k;

		// Case: incoming value is NaN...
		if ( isnan( x ) ) {
			N = W; // explicitly set to avoid `N < W` branch
			min = x;
			max = x;
		}
		// Case: initial window...
		else if ( N < W ) {
			N += 1;
			if ( x < min || ( x === min && isNegativeZero( x ) ) ) {
				min = x;
			}
			if ( x > max || ( x === max && isPositiveZero( x ) ) ) {
				max = x;
			}
		}
		// Case: outgoing value is the current minimum or maximum and the new value is either greater than the minimum or less than the maximum, and, thus, we need to find new accumulated values among the current buffer values...
		else if (
			( buf[ i ] === min && x > min ) ||
			( buf[ i ] === max && x < max ) ||
			isnan( buf[ i ] )
		) {
			min = x;
			max = x;
			for ( k = 0; k < W; k++ ) {
				if ( k !== i ) {
					v = buf[ k ];
					if ( isnan( v ) ) {
						min = v;
						max = v;
						break; // no need to continue searching
					}
					if ( v < min || ( v === min && isNegativeZero( v ) ) ) {
						min = v;
					}
					if ( v > max || ( v === max && isPositiveZero( v ) ) ) {
						max = v;
					}
				}
			}
		}
		// Case: incoming value is less than current minimum value...
		else if ( x < min ) {
			min = x;
		}
		// Case: incoming value is greater than current maximum value...
		else if ( x > max ) {
			max = x;
		}
		// Case: incoming value is zero, which means we need to be careful and correctly handle signed zeros...
		else if ( x === 0.0 ) {
			sgn = isNegativeZero( x );
			if ( x === min ) {
				// Case: outgoing value is the current minimum...
				if (
					buf[ i ] === min &&
					isNegativeZero( buf[ i ] ) &&
					sgn === false
				) {
					// Because the outgoing and incoming are different signs (-,+), we need to search the buffer to see if it contains a negative zero. If so, the minimum value remains negative zero; otherwise, the minimum value is incoming value...
					min = x;
					for ( k = 0; k < W; k++ ) {
						if ( k !== i && isNegativeZero( buf[ k ] ) ) {
							min = buf[ k ];
							break;
						}
					}
				} else if ( sgn ) {
					// Ensure minimum value has the correct sign:
					min = x;
				}
			}
			if ( x === max ) {
				// Case: outgoing value is the current maximum...
				if (
					buf[ i ] === max &&
					isPositiveZero( buf[ i ] ) &&
					sgn
				) {
					// Because the outgoing and incoming are different signs (+,-), we need to search the buffer to see if it contains a positive zero. If so, the maximum value remains positive zero; otherwise, the maximum value is incoming value...
					max = x;
					for ( k = 0; k < W; k++ ) {
						if ( k !== i && isPositiveZero( buf[ k ] ) ) {
							max = buf[ k ];
							break;
						}
					}
				} else if ( sgn === false ) {
					// Ensure maximum value has the correct sign:
					max = x;
				}
			}
		}
		// Case: updating existing window; however, the minimum and maximum values do not change so nothing to do...

		out[ 0 ] = min;
		out[ 1 ] = max;
		return out;
	}
Updates accumulator state.

@private
@param {number} x - input value
@param {NonNegativeInteger} i - buffer index
@returns {Collection} output array