Faster hex validation

benchmark/src/androidTest/java/com/vitorpamplona/quartz/benchmark/HexBenchmark.kt

@@ -23,6 +23,7 @@ package com.vitorpamplona.quartz.benchmark
 import androidx.benchmark.junit4.BenchmarkRule
 import androidx.benchmark.junit4.measureRepeated
 import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.vitorpamplona.quartz.encoders.HexValidator
 import junit.framework.TestCase.assertEquals
 import org.junit.Rule
 import org.junit.Test
@@ -65,4 +66,9 @@ class HexBenchmark {
 
         benchmarkRule.measureRepeated { assertEquals(testHex, fr.acinq.secp256k1.Hex.encode(bytes)) }
     }
+
+    @Test
+    fun isHex() {
+        benchmarkRule.measureRepeated { HexValidator.isHex(testHex) }
+    }
 }

quartz/src/main/java/com/vitorpamplona/quartz/encoders/HexUtils.kt

@@ -34,29 +34,9 @@ fun HexKey.hexToByteArray(): ByteArray {
 object HexValidator {
     private fun isHexChar(c: Char): Boolean {
         return when (c) {
-            '0',
-            '1',
-            '2',
-            '3',
-            '4',
-            '5',
-            '6',
-            '7',
-            '8',
-            '9',
-            'a',
-            'b',
-            'c',
-            'd',
-            'e',
-            'f',
-            'A',
-            'B',
-            'C',
-            'D',
-            'E',
-            'F',
-            -> true
+            in '0'..'9' -> true
+            in 'a'..'f' -> true
+            in 'A'..'F' -> true
             else -> false
         }
     }