Data commit

Task/Isqrt-integer-square-root-of-X/Go/isqrt-integer-square-root-of-x.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+    "fmt"
+    "log"
+    "math/big"
+)
+
+var zero = big.NewInt(0)
+var one = big.NewInt(1)
+
+func isqrt(x *big.Int) *big.Int {
+    if x.Cmp(zero) < 0 {
+        log.Fatal("Argument cannot be negative.")
+    }
+    q := big.NewInt(1)
+    for q.Cmp(x) <= 0 {
+        q.Lsh(q, 2)
+    }
+    z := new(big.Int).Set(x)
+    r := big.NewInt(0)
+    for q.Cmp(one) > 0 {
+        q.Rsh(q, 2)
+        t := new(big.Int)
+        t.Add(t, z)
+        t.Sub(t, r)
+        t.Sub(t, q)
+        r.Rsh(r, 1)
+        if t.Cmp(zero) >= 0 {
+            z.Set(t)
+            r.Add(r, q)
+        }
+    }
+    return r
+}
+
+func commatize(s string) string {
+    le := len(s)
+    for i := le - 3; i >= 1; i -= 3 {
+        s = s[0:i] + "," + s[i:]
+    }
+    return s
+}
+
+func main() {
+    fmt.Println("The integer square roots of integers from 0 to 65 are:")
+    for i := int64(0); i <= 65; i++ {
+        fmt.Printf("%d ", isqrt(big.NewInt(i)))
+    }
+    fmt.Println()
+    fmt.Println("\nThe integer square roots of powers of 7 from 7^1 up to 7^73 are:\n")
+    fmt.Println("power                                    7 ^ power                                                 integer square root")
+    fmt.Println("----- --------------------------------------------------------------------------------- -----------------------------------------")
+    pow7 := big.NewInt(7)
+    bi49 := big.NewInt(49)
+    for i := 1; i <= 73; i += 2 {
+        fmt.Printf("%2d %84s %41s\n", i, commatize(pow7.String()), commatize(isqrt(pow7).String()))
+        pow7.Mul(pow7, bi49)
+    }
+}