2016 Update

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-4.java

@@ -1 +1,12 @@
-def pairs: while( .[0] > 0; [ (.[0] | halve), (.[1] | double) ]);
+function ethMult(m, n) {
+  var o = !isNaN(m) ? 0 : ''; // same technique works with strings
+  if (n < 1) return o;
+  while (n > 1) {
+    if (n & 1) o += m;  // 3. integer odd/even? (bit-wise and 1)
+    n >>= 1;            // 1. integer halved (by right-shift)
+    m += m;             // 2. integer doubled (addition to self)
+  }
+  return o + m;
+}
+
+ethMult(17, 34)

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-5.java

@@ -1,15 +1 @@
-def halve: (./2) | floor;
-
-def double: 2 * .;
-
-def isEven: . % 2 == 0;
-
-def ethiopian_multiply(a;b):
-  def pairs: recurse( if .[0] > 0
-                      then [ (.[0] | halve), (.[1] | double) ]
-                      else empty
-                      end );
-  reduce ([a,b] | pairs
-          | select( .[0] | isEven | not)
-          | .[1] ) as $i
-    (0; . + $i) ;
+ethMult('Ethiopian', 34)

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-6.java

@@ -1 +1 @@
-ethiopian_multiply(17;34) # => 578
+def pairs: while( .[0] > 0; [ (.[0] | halve), (.[1] | double) ]);

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-7.java

@@ -0,0 +1,15 @@
+def halve: (./2) | floor;
+
+def double: 2 * .;
+
+def isEven: . % 2 == 0;
+
+def ethiopian_multiply(a;b):
+  def pairs: recurse( if .[0] > 0
+                      then [ (.[0] | halve), (.[1] | double) ]
+                      else empty
+                      end );
+  reduce ([a,b] | pairs
+          | select( .[0] | isEven | not)
+          | .[1] ) as $i
+    (0; . + $i) ;

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-8.java

@@ -0,0 +1 @@
+ethiopian_multiply(17;34) # => 578