YAPC::EU 2018 Glasgow Update!

Task/Arithmetic-geometric-mean-Calculate-Pi/Go/arithmetic-geometric-mean-calculate-pi.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+    "fmt"
+    "math/big"
+)
+
+func main() {
+    one := big.NewFloat(1)
+    two := big.NewFloat(2)
+    four := big.NewFloat(4)
+    prec := uint(768) // say
+
+    a := big.NewFloat(1).SetPrec(prec)
+    g := new(big.Float).SetPrec(prec)
+
+    // temporary variables
+    t := new(big.Float).SetPrec(prec)
+    u := new(big.Float).SetPrec(prec)
+
+    g.Quo(a, t.Sqrt(two))
+    sum := new(big.Float)
+    pow := big.NewFloat(2)
+
+    for a.Cmp(g) != 0 {
+        t.Add(a, g)
+        t.Quo(t, two)
+        g.Sqrt(u.Mul(a, g))
+        a.Set(t)
+        pow.Mul(pow, two)
+        t.Sub(t.Mul(a, a), u.Mul(g, g))
+        sum.Add(sum, t.Mul(t, pow))
+    }
+
+    t.Mul(a, a)
+    t.Mul(t, four)
+    pi := t.Quo(t, u.Sub(one, sum))
+    fmt.Println(pi)
+}