function accumulator( x ) {
		var v;
		var k;
		if ( arguments.length === 0 ) {
			if ( N === 0 ) {
				return null;
			}
			return min;
		}
		// Update the index for managing the circular buffer:
		i = (i+1) % W;

		// Case: update initial window...
		if ( N < W ) {
			N += 1;
			if (
				isnan( x ) ||
				x < min ||
				( x === min && isNegativeZero( x ) )
			) {
				min = x;
			}
		}
		// Case: incoming value is NaN or less than current minimum value...
		else if ( isnan( x ) || x < min ) {
			min = x;
		}
		// Case: outgoing value is the current minimum and the new value is greater than the minimum, and, thus, we need to find a new minimum among the current values...
		else if ( ( buf[ i ] === min && x > min ) || isnan( buf[ i ] ) ) {
			min = x;
			for ( k = 0; k < W; k++ ) {
				if ( k !== i ) {
					v = buf[ k ];
					if ( isnan( v ) ) {
						min = v;
						break; // no need to continue searching
					}
					if ( v < min || ( v === min && isNegativeZero( v ) ) ) {
						min = v;
					}
				}
			}
		}
		// Case: outgoing value is the current minimum, which is zero, and the new value is also zero, and, thus, we need to correctly handle signed zeros...
		else if ( buf[ i ] === min && x === min && x === 0.0 ) {
			if ( isNegativeZero( x ) ) {
				min = x;
			} else if ( isNegativeZero( buf[ i ] ) ) {
				// 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;
					}
				}
			}
			// Case: the outgoing and incoming values are both positive zero, so nothing changes
		}
		// Case: updating existing window; however, the minimum value does not change so nothing to do but update our buffer...

		buf[ i ] = x;
		return min;
	}
If provided a value, the accumulator function returns an updated minimum. If not provided a value, the accumulator function returns the current minimum.

@private
@param {number} [x] - input value
@returns {(number|null)} minimum value or null