got rid of regexp in guards (#129)

guards/guards.go

@@ -6,41 +6,56 @@ import (
 	"github.com/iotaledger/iota.go/curl"
 	. "github.com/iotaledger/iota.go/trinary"
 
-	"regexp"
 )
 
 // IsTrytes checks if input is correct trytes consisting of [9A-Z]
 func IsTrytes(trytes Trytes) bool {
 	if len(trytes) < 1 {
 		return false
 	}
-	match, _ := regexp.MatchString("^[9A-Z]+$", string(trytes))
-	return match
+	for _, runeVal := range trytes {
+		if (runeVal < 'A' || runeVal > 'Z') && runeVal != '9' {
+			return false
+		}
+	}
+	return true
 }
 
 // IsTrytesOfExactLength checks if input is correct trytes consisting of [9A-Z] and given length
 func IsTrytesOfExactLength(trytes Trytes, length int) bool {
-	if len(trytes) != length {
+	if len(trytes) != length || len(trytes) == 0 {
 		return false
 	}
-	match, _ := regexp.MatchString("^[9A-Z]+$", string(trytes))
-	return match
+        for _, runeVal := range trytes {
+                if (runeVal < 'A' || runeVal > 'Z') && runeVal != '9' {
+                        return false
+                }
+        }
+        return true
 }
 
 // IsTrytesOfMaxLength checks if input is correct trytes consisting of [9A-Z] and length <= maxLength
 func IsTrytesOfMaxLength(trytes Trytes, max int) bool {
 	if len(trytes) > max || len(trytes) < 1 {
 		return false
 	}
-	match, _ := regexp.MatchString("^[9A-Z]+$", string(trytes))
-	return match
+        for _, runeVal := range trytes {
+                if (runeVal < 'A' || runeVal > 'Z') && runeVal != '9' {
+                        return false
+                }
+        }
+        return true
 }
 
-var onlyNinesRegex = regexp.MustCompile("^[9]+$")
-
 // IsEmptyTrytes checks if input is null (all 9s trytes)
 func IsEmptyTrytes(trytes Trytes) bool {
-	return onlyNinesRegex.MatchString(string(trytes))
+        for _, runeVal := range trytes {
+                if runeVal != '9' {
+                        return false
+                }
+        }
+
+        return true
 }
 
 // IsHash checks if input is correct hash (81 trytes or 90)