function nullaryBlockSize( dtypeX ) {
	var nbx = bytesPerElement( dtypeX );
	if ( nbx === null ) { // e.g., "generic" arrays
		return defaults.BLOCK_SIZE_IN_ELEMENTS;
	}
	return ( defaults.BLOCK_SIZE_IN_BYTES/nbx )|0; // asm type annotation
}
Returns a loop block size for multi-dimensional array tiled loops.

@param {string} dtypeX - array data type
@returns {integer} block size (in units of elements)

@example
var bsize = nullaryBlockSize( 'float64' );
// returns <number>