Micro-optimisations to perform better on JSON and String processing (#1280)

Author: djinn

quickjs.c

@@ -20185,7 +20185,7 @@ typedef struct JSFunctionDef {
     bool need_home_object : 1;
     bool use_short_opcodes : 1; /* true if short opcodes are used in byte_code */
     bool has_await : 1; /* true if await is used (used in module eval) */
-    
+
     JSFunctionKindEnum func_kind : 8;
     JSParseFunctionEnum func_type : 7;
     uint8_t is_strict_mode : 1;
@@ -20344,6 +20344,21 @@ static const JSOpCode opcode_info[OP_COUNT + (OP_TEMP_END - OP_TEMP_START)] = {
     opcode_info[(op) >= OP_TEMP_START ? \
                 (op) + (OP_TEMP_END - OP_TEMP_START) : (op)]
 
+static void json_free_token(JSParseState *s, JSToken *token) {
+    // Only free actual allocated values
+    switch(token->val) {
+    case TOK_NUMBER:
+        JS_FreeValue(s->ctx, token->u.num.val);
+        break;
+    case TOK_STRING:
+        JS_FreeValue(s->ctx, token->u.str.str);
+        break;
+    case TOK_IDENT:
+        JS_FreeAtom(s->ctx, token->u.ident.atom);
+        break;
+    }
+}
+
 static void free_token(JSParseState *s, JSToken *token)
 {
     switch(token->val) {
@@ -21425,14 +21440,30 @@ static int json_parse_string(JSParseState *s, const uint8_t **pp)
     uint32_t c;
     StringBuffer b_s, *b = &b_s;
 
-    if (string_buffer_init(s->ctx, b, 32))
+    if (string_buffer_init(s->ctx, b, 48))
         goto fail;
 
     p = *pp;
     for(;;) {
         if (p >= s->buf_end) {
             goto end_of_input;
         }
+
+        // Fast path: batch consecutive ASCII characters
+        const uint8_t *p_start = p;
+        while (p < s->buf_end && *p != '"' && *p != '\\' && *p >= 0x20 && *p < 0x80) {
+            p++;
+        }
+
+        // Write batched ASCII in one call
+        if (p > p_start) {
+            if (string_buffer_write8(b, p_start, p - p_start))
+                goto fail;
+        }
+
+        if (p >= s->buf_end)
+            goto end_of_input;
+
         c = *p++;
         if (c == '"')
             break;
@@ -21578,7 +21609,7 @@ static __exception int json_next_token(JSParseState *s)
         return -1;
     }
 
-    free_token(s, &s->token);
+    json_free_token(s, &s->token);
 
     p = s->last_ptr = s->buf_ptr;
     s->last_line_num = s->token.line_num;