Initial data commit

Task/Modular-inverse/VBA/modular-inverse.vba

@@ -0,0 +1,31 @@
+Private Function mul_inv(a As Long, n As Long) As Variant
+    If n < 0 Then n = -n
+    If a < 0 Then a = n - ((-a) Mod n)
+    Dim t As Long: t = 0
+    Dim nt As Long: nt = 1
+    Dim r As Long: r = n
+    Dim nr As Long: nr = a
+    Dim q As Long
+    Do While nr <> 0
+        q = r \ nr
+        tmp = t
+        t = nt
+        nt = tmp - q * nt
+        tmp = r
+        r = nr
+        nr = tmp - q * nr
+    Loop
+    If r > 1 Then
+        mul_inv = "a is not invertible"
+    Else
+        If t < 0 Then t = t + n
+        mul_inv = t
+    End If
+End Function
+Public Sub mi()
+    Debug.Print mul_inv(42, 2017)
+    Debug.Print mul_inv(40, 1)
+    Debug.Print mul_inv(52, -217) '/* Pari semantics for negative modulus */
+    Debug.Print mul_inv(-486, 217)
+    Debug.Print mul_inv(40, 2018)
+End Sub