Data commit

Task/Modular-inverse/ERRE/modular-inverse.erre

@@ -0,0 +1,26 @@
+PROGRAM MOD_INV
+
+!$INTEGER
+
+PROCEDURE MUL_INV(A,B->T)
+  LOCAL NT,R,NR,Q,TMP
+  IF B<0 THEN B=-B
+  IF A<0 THEN A=B-(-A MOD B)
+  T=0  NT=1  R=B  NR=A MOD B
+  WHILE NR<>0 DO
+      Q=R DIV NR
+      TMP=NT  NT=T-Q*NT  T=TMP
+      TMP=NR  NR=R-Q*NR  R=TMP
+  END WHILE
+  IF (R>1) THEN T=-1 EXIT PROCEDURE  ! NO INVERSE
+  IF (T<0) THEN T+=B
+END PROCEDURE
+
+
+BEGIN
+     MUL_INV(42,2017->T) PRINT(T)
+     MUL_INV(40,1->T) PRINT(T)
+     MUL_INV(52,-217->T) PRINT(T)    ! pari semantics for negative modulus
+     MUL_INV(-486,217->T)  PRINT(T)
+     MUL_INV(40,2018->T) PRINT(T)
+END PROGRAM