factors: Remove most panics

Panics are not the best way of handling errors in Go.  I've replaced
panics with default values whenever a sensible one exists.
Factors(0) does not have a sensible default value (as every number is a
factor of zero), so it still panics.

1 files changed, 12 insertions, 8 deletions

diff --git a/factors/digit_map.go b/factors/digit_map.go
index 83606e9..a16f018 100644
--- a/factors/digit_map.go
+++ b/factors/digit_map.go
@@ -28,6 +28,7 @@ const (
 	// - it will not be nice to work with
 	Opaque TotativeType = 0x40
 	// This number is zero, and doesn't have a true totative type.
+	// (except in radix zero, where zero is considered a factor)
 	Zero TotativeType = 0x00
 )
 
@@ -98,6 +99,10 @@ func Split(digit, radix uint) (regular, totative uint) {
 
 // Calculates the regularity index of a number's regular part
 func calcRegularity(regular, radix uint) uint8 {
+	if regular == 0 && radix == 0 {
+		return 1
+	}
+
 	regularity, radixPower := uint8(0), uint(1)
 	for radixPower%regular != 0 {
 		regularity++
@@ -125,10 +130,8 @@ func calcTotativeType(totative, radix uint) TotativeType {
 }
 
 // Gets the regularity and totative type of one digit in a radix
+// In radix zero, zero is type 1R, one is type 0R, and everything else is 0P.
 func GetDigitType(digit, radix uint) DigitType {
-	if radix < 2 {
-		panic("Radices cannot be less than 2!")
-	}
 	radixPF := PrimeFactorize(radix)
 	digitPF := PrimeFactorize(digit)
 	regular, totative := splitPF(digitPF, radixPF)
@@ -139,13 +142,14 @@ func GetDigitType(digit, radix uint) DigitType {
 
 // Gets the regularity and totative type of each digit in a radix
 func DigitMap(radix uint) []DigitType {
-	if radix < 2 {
-		panic("Radices cannot be less than 2!")
-	}
 	radixPF := PrimeFactorize(radix)
 	types := make([]DigitType, radix, radix)
-	types[0] = zeroType
-	types[1] = oneType
+	if radix > 0 {
+		types[0] = zeroType
+	}
+	if radix > 1 {
+		types[1] = oneType
+	}
 	for d := uint(2); d < radix; d++ {
 		digitPF := PrimeFactorize(d)
 		regular, totative := splitPF(digitPF, radixPF)