First commit of partial RosettaCode contents.

Pushing this for testing purposes. Lots of work still needed.

Task/Pi/Go/pi.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+    "fmt"
+    "math/big"
+)
+
+type lft struct {
+    q,r,s,t big.Int
+}
+
+func (t *lft) extr(x *big.Int) *big.Rat {
+    var n, d big.Int
+    var r big.Rat
+    return r.SetFrac(
+        n.Add(n.Mul(&t.q, x), &t.r),
+        d.Add(d.Mul(&t.s, x), &t.t))
+}
+
+var three = big.NewInt(3)
+var four = big.NewInt(4)
+
+func (t *lft) next() *big.Int {
+    r := t.extr(three)
+    var f big.Int
+    return f.Div(r.Num(), r.Denom())
+}
+
+func (t *lft) safe(n *big.Int) bool {
+    r := t.extr(four)
+    var f big.Int
+    if n.Cmp(f.Div(r.Num(), r.Denom())) == 0 {
+        return true
+    }
+    return false
+}
+
+func (t *lft) comp(u *lft) *lft {
+    var r lft
+    var a, b big.Int
+    r.q.Add(a.Mul(&t.q, &u.q), b.Mul(&t.r, &u.s))
+    r.r.Add(a.Mul(&t.q, &u.r), b.Mul(&t.r, &u.t))
+    r.s.Add(a.Mul(&t.s, &u.q), b.Mul(&t.t, &u.s))
+    r.t.Add(a.Mul(&t.s, &u.r), b.Mul(&t.t, &u.t))
+    return &r
+}
+
+func (t *lft) prod(n *big.Int) *lft {
+    var r lft
+    r.q.SetInt64(10)
+    r.r.Mul(r.r.SetInt64(-10), n)
+    r.t.SetInt64(1)
+    return r.comp(t)
+}
+
+func main() {
+    // init z to unit
+    z := new(lft)
+    z.q.SetInt64(1)
+    z.t.SetInt64(1)
+
+    // lfts generator
+    var k int64
+    lfts := func() *lft {
+        k++
+        r := new(lft)
+        r.q.SetInt64(k)
+        r.r.SetInt64(4*k+2)
+        r.t.SetInt64(2*k+1)
+        return r
+    }
+
+    // stream
+    for {
+        y := z.next()
+        if z.safe(y) {
+            fmt.Print(y)
+            z = z.prod(y)
+        } else {
+            z = z.comp(lfts())
+        }
+    }
+}