Ethiopian multiplication: Difference between revisions

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 =={{header|C}}==
 <lang c>#include <stdio.h>
+#include <stdbool.h>
-int ethiopian(int left, int right)
+void halve(int *x) { *x >>= 1; }
+void doublit(int *x)  { *x <<= 1; }
+bool iseven(const int x) { return (x & 1) ==  0; }
+int ethiopian(int plier,
+	      int plicand, const bool tutor)
 {
-	int result = 0;
+  int result=0;
-	for (; left; left >>= 1, right <<= 1, printf("\n")) {
-		printf("%4d %6d", left, right);
+  if (tutor)
-		if (left & 1) result += right;
-		else	      printf(" X");
+    printf("ethiopian multiplication of %d by %d\n", plier, plicand);
-	}
+  while(plier >= 1) {
-	printf("-------------\n      %5d\n", result);
+    if ( iseven(plier) ) {
-	return result;
+      if (tutor) printf("%4d %6d struck\n", plier, plicand);
+    } else {
+      if (tutor) printf("%4d %6d kept\n", plier, plicand);
+      result += plicand;
+    }
+    halve(&plier); doublit(&plicand);
+  }
+  return result;
 }
 int main()
 {
-	ethiopian(17, 34);
+  printf("%d\n", ethiopian(17, 34, true));
-	return 0;
+  return 0;
 }</lang>