Ethiopian multiplication: Difference between revisions

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 :[http://www.ncetm.org.uk/blogs/3064 Ethiopian multiplication]
 :[http://www.bbc.co.uk/dna/h2g2/A22808126 Russian Peasant Multiplication]
+=={{header|C}}==
+<lang c>#include <stdio.h>
+#include <stdbool.h>
+void halve(int *x) { *x >>= 1; }
+void doublit(int *x)  { *x <<= 1; }
+bool iseven(const int x) { return (x%2) == 0; }
+int ethiopian(int plier,
+	      int plicand, const bool tutor)
+{
+  int result=0;
+  if (tutor)
+    printf("ethiopian multiplication of %d by %d\n", plier, plicand);
+  while(plier >= 1) {
+    if ( iseven(plier) ) {
+      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()
+{
+  printf("%d\n", ethiopian(17, 34, true));
+  return 0;
+}</lang>
 =={{header|Python}}==