awk to divide fields based on match in file1 - awk

Question

I am trying to use awk to do the below steps
find matching fields $1 strings between file1 and file2
if the $1 strings match then $2 in file1 is divided by $3 in file2 (that is x which is 3 signifigant figures rounded up)
x is multiplied by 100
each x is subtracted from 100 and that is the %
file1
USH2A 21
GIT1 357
PALB2 3
file2
GIT1 21 3096
USH2A 71 17718
PALB2 13 3954
awk
awk 'NR==FNR{a[$1]=$1;next;}{if ($1 in a) print $1, $2/a[$3];else print;}' file2 file1 > test
awk: cmd. line:1: (FILENAME=search FNR=2) fatal: division by zero attempted
awk 'NR==FNR{a[$1]=$1;next;}{if ($1 in a) print $1, $2/a[$3];else print;}' file1 file2 > test
awk: cmd. line:1: (FILENAME=search FNR=1) fatal: division by zero attempted
example
USH2A match is found so (21/17718)*100 = 0.11 and 100-0.11 = 99.99%
GIT1 match is found so (357/3096)*100 = 11.53 and 100-11.53 = 88.47%
PALB2 match is found so (3/3954) *100 = 0.07 and 100-0.7 = 99.93%
I am going line by line in the code and can see that I am already getting errors. Thank you :).

Answer 1

awk to the rescue!
$ awk 'function ceil(v) {return int(v)==v?v:int(v+1)}
NR==FNR{f1[$1]=$2; next}
$1 in f1{print $1, ceil(10000*(1-f1[$1]/$3))/100 "%"}' file1 file2
GIT1 88.47%
USH2A 99.89%
PALB2 99.93%
note that there is no round-up in awk so defined a ceil function for this task.

Answer 2

$ cat tst.awk
NR==FNR { a[$1]=$3; next }
$1 in a {
x = (a[$1] ? ($2*100)/a[$1] : 0)
printf "%s match is found so (%d/%d) *100 = %.2f and 100-%.2f = %.2f%%\n", $1, $2, a[$1], x, x, 100-x
}
$ awk -f tst.awk file2 file1
USH2A match is found so (21/17718) *100 = 0.12 and 100-0.12 = 99.88%
GIT1 match is found so (357/3096) *100 = 11.53 and 100-11.53 = 88.47%
PALB2 match is found so (3/3954) *100 = 0.08 and 100-0.08 = 99.92%