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go/trinary/trinary.go

@@ -2,30 +2,32 @@ package trinary
 
 import (
 	"errors"
-	"fmt"
-	"math"
+	"math/big"
 )
 
 // ParseTrinary takes a trinary string and returns the
 // decimal value
 func ParseTrinary(in string) (int64, error) {
-	fmt.Println("=== New Parse (" + in + ") ===")
-	var ret int
-	place := len(in)
-
-	for i := range in {
-		fmt.Print("Finding ", (place - i), " place value ", string(in[i]))
-		switch in[i] {
-		case '0':
-		case '1':
-			ret = ret + ((place - i) * 3)
-		case '2':
-			ret = ret + ((place - i) * int(math.Pow(3, 2)))
-		default:
-			return 0, errors.New("Invalid String")
-		}
-		fmt.Println("==", ret)
-		place--
-	}
-	return int64(ret), nil
+	return convertNumStringBase(in, int64(3))
+}
+
+// convertNumStringBase takes a numeric string and the base of that string
+// and returns an int64 of the decimal representation
+func convertNumStringBase(in string, oldBase int64) (int64, error) {
+	base := big.NewInt(oldBase)
+	var sum big.Int
+	for i := range in {
+		x := big.NewInt(int64(in[i] - '0'))
+		pow := big.NewInt(int64(len(in) - i - 1))
+
+		var n big.Int
+		n.Exp(base, pow, nil)
+		n.Mul(x, &n)
+
+		sum.Add(&sum, &n)
+		if sum.Int64() < 0 {
+			return 0, errors.New("Integer Overflow")
+		}
+	}
+	return sum.Int64(), nil
 }