Initial data commit

Task/Modular-inverse/UNIX-Shell/modular-inverse.sh

@@ -0,0 +1,24 @@
+function invmod {
+  typeset -i a=$1 n=$2
+  if (( n < 0 )); then (( n = -n )); fi
+  if (( a < 0 )); then (( a = n - (-a) % n )); fi
+
+  typeset -i t=0 nt=1 r=n nr q tmp
+  (( nr = a % n ))
+  while ((  nr )); do
+    (( q = r/nr ))
+    (( tmp = nt ))
+    (( nt = t - q*nt ))
+    (( t = tmp ))
+    (( tmp = nr ))
+    (( nr = r - q*nr ))
+    (( r = tmp ))
+  done
+  if (( r > 1 )); then
+    return 1
+  fi
+  while (( t < 0 )); do (( t += n )); done
+  printf '%s\n' "$t"
+}
+
+invmod 42 2017