It's possible to use a mapping like this:
inoremap <silent> sf <c-r><c-r>=getline('.')->strcharpart(0,getpos('.')[2]-1)->substitute('.*;','','')->substitute('=.*','','')->trim()<cr>
(For older version where "method call" is not available it's possible to use
inoremap <silent> sf <c-r><c-r>=trim(substitute(substitute(strcharpart(getline('.'),0,getpos('.')[2]-1),'.*;','',''),'=.*','',''))
instead)
So you only need to type
table[row][col] = std::max(sf, other_table[row+1][col+1])
The sf typed will expand to table[row][col] in this case.