new files

Task/Ackermann-function/Go/ackermann-function-1.go

@@ -0,0 +1,9 @@
+func Ackermann(m, n uint) uint {
+  switch {
+    case m == 0:
+      return n + 1
+    case n == 0:
+      return Ackermann(m - 1, 1)
+  }
+  return Ackermann(m - 1, Ackermann(m, n - 1))
+}

Task/Ackermann-function/Go/ackermann-function-2.go

@@ -0,0 +1,15 @@
+func Ackermann2(m, n uint) uint {
+  switch {
+    case m == 0:
+      return n + 1
+    case m == 1:
+      return n + 2
+    case m == 2:
+      return 2*n + 3
+    case m == 3:
+      return 8 << n - 3
+    case n == 0:
+      return Ackermann2(m - 1, 1)
+  }
+  return Ackermann2(m - 1, Ackermann2(m, n - 1))
+}

Task/Ackermann-function/Go/ackermann-function-3.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+    "fmt"
+    "math/big"
+    "unsafe"
+)
+
+var one = big.NewInt(1)
+var two = big.NewInt(2)
+var three = big.NewInt(3)
+var eight = big.NewInt(8)
+var u uint
+var uBits = int(unsafe.Sizeof(u))*8 - 1
+
+func Ackermann2(m, n *big.Int) *big.Int {
+    if m.Cmp(three) <= 0 {
+        switch m.Int64() {
+        case 0:
+            return new(big.Int).Add(n, one)
+        case 1:
+            return new(big.Int).Add(n, two)
+        case 2:
+            r := new(big.Int).Lsh(n, 1)
+            return r.Add(r, three)
+        case 3:
+            if n.BitLen() > uBits {
+                panic("way too big")
+            }
+            r := new(big.Int).Lsh(eight, uint(n.Int64()))
+            return r.Sub(r, three)
+        }
+    }
+    if n.BitLen() == 0 {
+        return Ackermann2(new(big.Int).Sub(m, one), one)
+    }
+    return Ackermann2(new(big.Int).Sub(m, one),
+        Ackermann2(m, new(big.Int).Sub(n, one)))
+}
+
+func main() {
+    show(0, 0)
+    show(1, 2)
+    show(2, 4)
+    show(3, 100)
+    show(4, 1)
+    show(4, 3)
+}
+
+func show(m, n int64) {
+    fmt.Printf("A(%d, %d) = ", m, n)
+    fmt.Println(Ackermann2(big.NewInt(m), big.NewInt(n)))
+}