move to lib

cmd/divisor.go

@@ -21,27 +21,9 @@ import (
 	"math/big"
 
 	"github.com/spf13/cobra"
+	"scm.dairydemon.net/filifa/mathtools/internal/lib"
 )
 
-// TODO: expand to work for different sigmas
-func divisorSummatory(n *big.Int) *big.Int {
-	// employing Dirichlet's hyperbola method
-	sqrt := new(big.Int).Sqrt(n)
-
-	total := big.NewInt(0)
-	for x := big.NewInt(1); x.Cmp(sqrt) <= 0; x.Add(x, big.NewInt(1)) {
-		z := new(big.Int).Div(n, x)
-		total.Add(total, z)
-	}
-
-	total.Mul(total, big.NewInt(2))
-
-	sqrt.Exp(sqrt, big.NewInt(2), nil)
-	total.Sub(total, sqrt)
-
-	return total
-}
-
 func divisorSum(cmd *cobra.Command, args []string) {
 	for _, arg := range args {
 		n, ok := new(big.Int).SetString(arg, 10)
@@ -50,7 +32,7 @@ func divisorSum(cmd *cobra.Command, args []string) {
 			continue
 		}
 
-		d := divisorSummatory(n)
+		d := lib.DivisorSummatory(n)
 		fmt.Println(d)
 	}
 }