Reuse some functions and fix a bug

Author: wooster0

lib/std/ascii.zig

@@ -67,17 +67,15 @@ fn isControlNaive(char: u8) bool {
     return char <= control.US or char == control.DEL;
 }
 fn isAlphabeticNaive(char: u8) bool {
-    return (char >= 'a' and char <= 'z') or (char >= 'Z' and char <= 'Z');
+    return isLower(char) or isUpper(char);
 }
 fn isHexadecimalNaive(char: u8) bool {
-    return (char >= '0' and char <= '9') or
+    return isDigit(char) or
         (char >= 'a' and char <= 'f') or
         (char >= 'A' and char <= 'F');
 }
 fn isAlphanumericNaive(char: u8) bool {
-    return (char >= '0' and char <= '9') or
-        (char >= 'a' and char <= 'z') or
-        (char >= 'A' and char <= 'Z');
+    return isDigit(char) or isAlphabeticNaive(char);
 }
 fn isWhitespaceNaive(char: u8) bool {
     @setEvalBranchQuota(4000);
@@ -246,7 +244,7 @@ test "ascii character classes" {
     try testing.expect('\xab' == toUpper('\xab'));
     try testing.expect(!isUpper('z'));
 
-    try testing.expect('c' == toLower('c'));
+    try testing.expect('c' == toLower('C'));
     try testing.expect(':' == toLower(':'));
     try testing.expect('\xab' == toLower('\xab'));
     try testing.expect(!isLower('Z'));