calculate the sum of all values from 1 to end , including . that is : sum = 1 + 2 + 3 + ... + end-1 + end examples : f 0 = 0 f 1 = 1 f 2 = 3 f 3 = 6 f 10 = 55 f 100 = 5050 concode_field_sep PlaceHolder placeHolder concode_field_sep long ceilDiv concode_elem_sep int ceilDiv concode_elem_sep boolean isAddUnderOrOverflow concode_elem_sep long unsignedAdd concode_elem_sep int clip concode_elem_sep long clip concode_elem_sep double clip
long function ( long arg0 ) { if ( arg0 < 1 ) return 0 ; return ( arg0 * ( arg0 + 1 ) ) / 2 ; }