excel - Search String in large Range, return row number -

i trying write function search string in range of 4,500 columns , 100 rows , return row match in. formula copied 6k cells , needs continually updated worksheet hence function.

i've tried using search.find function , returning row number it's slow. here's code i've used:

function findrow(srch string, srchrng)  dim rngsearch range, rngfound range  set rngsearch = srchrng set rngfound = rngsearch.find(what:=srch, lookin:=xlvalues, lookat:=xlpart, searchorder:=xlbycolumns) if rngfound nothing findrow = "#n/a" else findrow = rngfound.row end if  end function 

some more details of issue:

-string must exact match , 50 characters long

-range i'm searching on has many blank cells, 1 exact match.