1 files changed, 15 insertions, 13 deletions
diff --git a/internal/jsonparse/parse.go b/internal/jsonparse/parse.go
index 73584d9..2f5c1ab 100644
--- a/internal/jsonparse/parse.go
+++ b/internal/jsonparse/parse.go
@@ -14,6 +14,12 @@ import (
 
 var ErrParserExceededMaxDepth = errors.New("exceeded max depth")
 
+func isHex(c rune) bool {
+	return ('0' <= c && c <= '9') ||
+		('a' <= c && c <= 'f') ||
+		('A' <= c && c <= 'F')
+}
+
 // RuneType is the classification of a rune when parsing JSON input.
 // A Parser, rather than grouping runes into tokens and classifying
 // tokens, classifies runes directly.
@@ -667,30 +673,26 @@ func (par *Parser) HandleRune(c rune) (RuneType, error) {
 			return RuneTypeError, fmt.Errorf("string backslash sequence: unexpected character: %q", c)
 		}
 	case RuneTypeStringEscU:
-		if _, ok := HexToInt(c); ok {
-			return par.replaceState(RuneTypeStringEscUA), nil
-		} else {
+		if !isHex(c) {
 			return RuneTypeError, fmt.Errorf("string unicode sequence: unexpected character: %q", c)
 		}
+		return par.replaceState(RuneTypeStringEscUA), nil
 	case RuneTypeStringEscUA:
-		if _, ok := HexToInt(c); ok {
-			return par.replaceState(RuneTypeStringEscUB), nil
-		} else {
+		if !isHex(c) {
 			return RuneTypeError, fmt.Errorf("string unicode sequence: unexpected character: %q", c)
 		}
+		return par.replaceState(RuneTypeStringEscUB), nil
 	case RuneTypeStringEscUB:
-		if _, ok := HexToInt(c); ok {
-			return par.replaceState(RuneTypeStringEscUC), nil
-		} else {
+		if !isHex(c) {
 			return RuneTypeError, fmt.Errorf("string unicode sequence: unexpected character: %q", c)
 		}
+		return par.replaceState(RuneTypeStringEscUC), nil
 	case RuneTypeStringEscUC:
-		if _, ok := HexToInt(c); ok {
-			par.replaceState(RuneTypeStringBeg)
-			return RuneTypeStringEscUD, nil
-		} else {
+		if !isHex(c) {
 			return RuneTypeError, fmt.Errorf("string unicode sequence: unexpected character: %q", c)
 		}
+		par.replaceState(RuneTypeStringBeg)
+		return RuneTypeStringEscUD, nil
 	// number //////////////////////////////////////////////////////////////////////////////////
 	//
 	// Here's a flattened drawing of the syntax diagram from www.json.org :