output solutions based on repetend period

cmd/pell.go

@@ -26,16 +26,6 @@ import (
 
 var pellCoeff string
 
-func isPellSolution(h, k, d *big.Int) bool {
-	foo := new(big.Int).Exp(k, big.NewInt(2), nil)
-	foo.Mul(d, foo)
-
-	bar := new(big.Int).Exp(h, big.NewInt(2), nil)
-	bar.Sub(bar, foo)
-
-	return bar.Cmp(big.NewInt(1)) == 0
-}
-
 func pell(cmd *cobra.Command, args []string) {
 	d, ok := new(big.Int).SetString(pellCoeff, 10)
 	if !ok {
@@ -49,12 +39,20 @@ func pell(cmd *cobra.Command, args []string) {
 		cobra.CheckErr(pellCoeff + " is a perfect square")
 	}
 
+	r := len(repetend)
+	var period int
+	if r%2 == 0 {
+		period = r
+	} else {
+		period = 2 * r
+	}
+
 	hch := gaussianBrackets(a0, big.NewInt(1), cycle(repetend))
 	kch := gaussianBrackets(big.NewInt(1), big.NewInt(0), cycle(repetend))
 
-	for {
+	for i := 1; true; i = (i + 1) % period {
 		h, k := <-hch, <-kch
-		if isPellSolution(h, k, d) {
+		if i == period-1 {
 			fmt.Println(h, k)
 		}
 	}