zero copy C literal strings in symbol table

include/mruby.h

@@ -230,6 +230,8 @@ mrb_value mrb_funcall_argv(mrb_state*, mrb_value, mrb_sym, int, mrb_value*);
 mrb_value mrb_funcall_with_block(mrb_state*, mrb_value, mrb_sym, int, mrb_value*, mrb_value);
 mrb_sym mrb_intern_cstr(mrb_state*,const char*);
 mrb_sym mrb_intern(mrb_state*,const char*,size_t);
+mrb_sym mrb_intern_literal(mrb_state*,const char*,size_t);
+#define mrb_intern_lit(mrb, lit) mrb_intern_literal(mrb, (lit), sizeof(lit) - 1)
 mrb_sym mrb_intern_str(mrb_state*,mrb_value);
 mrb_value mrb_check_intern_cstr(mrb_state*,const char*);
 mrb_value mrb_check_intern(mrb_state*,const char*,size_t);
@@ -239,8 +241,6 @@ const char *mrb_sym2name_len(mrb_state*,mrb_sym,size_t*);
 mrb_value mrb_sym2str(mrb_state*,mrb_sym);
 mrb_value mrb_str_format(mrb_state *, int, const mrb_value *, mrb_value);
 
-#define mrb_intern_lit(mrb, lit) mrb_intern(mrb, (lit), sizeof(lit) - 1)
-
 void *mrb_malloc(mrb_state*, size_t);         /* raise RuntimeError if no mem */
 void *mrb_calloc(mrb_state*, size_t, size_t); /* ditto */
 void *mrb_realloc(mrb_state*, void*, size_t); /* ditto */

src/symbol.c

@@ -13,7 +13,8 @@
 
 /* ------------------------------------------------------ */
 typedef struct symbol_name {
-  size_t len;
+  mrb_bool lit;
+  uint16_t len;
   const char *name;
 } symbol_name;
 
@@ -34,8 +35,8 @@ sym_hash_func(mrb_state *mrb, const symbol_name s)
 KHASH_DECLARE(n2s, symbol_name, mrb_sym, 1)
 KHASH_DEFINE (n2s, symbol_name, mrb_sym, 1, sym_hash_func, sym_hash_equal)
 /* ------------------------------------------------------ */
-mrb_sym
-mrb_intern(mrb_state *mrb, const char *name, size_t len)
+static mrb_sym
+sym_intern(mrb_state *mrb, const char *name, size_t len, int lit)
 {
   khash_t(n2s) *h = mrb->name2sym;
   symbol_name sname;
@@ -43,6 +44,10 @@ mrb_intern(mrb_state *mrb, const char *name, size_t len)
   mrb_sym sym;
   char *p;
 
+  if (len > UINT16_MAX) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "symbol length too long");
+  }
+  sname.lit = lit;
   sname.len = len;
   sname.name = name;
   k = kh_get(n2s, mrb, h, sname);
@@ -50,16 +55,33 @@ mrb_intern(mrb_state *mrb, const char *name, size_t len)
     return kh_value(h, k);
 
   sym = ++mrb->symidx;
-  p = (char *)mrb_malloc(mrb, len+1);
-  memcpy(p, name, len);
-  p[len] = 0;
-  sname.name = (const char*)p;
+  if (lit) {
+    sname.name = name;
+  }
+  else {
+    p = (char *)mrb_malloc(mrb, len+1);
+    memcpy(p, name, len);
+    p[len] = 0;
+    sname.name = (const char*)p;
+  }
   k = kh_put(n2s, mrb, h, sname);
   kh_value(h, k) = sym;
 
   return sym;
 }
 
+mrb_sym
+mrb_intern(mrb_state *mrb, const char *name, size_t len)
+{
+  return sym_intern(mrb, name, len, 0);
+}
+
+mrb_sym
+mrb_intern_literal(mrb_state *mrb, const char *name, size_t len)
+{
+  return sym_intern(mrb, name, len, 1);
+}
+
 mrb_sym
 mrb_intern_cstr(mrb_state *mrb, const char *name)
 {
@@ -79,6 +101,9 @@ mrb_check_intern(mrb_state *mrb, const char *name, size_t len)
   symbol_name sname;
   khiter_t k;
 
+  if (len > UINT16_MAX) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "symbol length too long");
+  }
   sname.len = len;
   sname.name = name;
 
@@ -129,7 +154,13 @@ mrb_free_symtbl(mrb_state *mrb)
   khiter_t k;
 
   for (k = kh_begin(h); k != kh_end(h); k++)
-    if (kh_exist(h, k)) mrb_free(mrb, (char*)kh_key(h, k).name);
+    if (kh_exist(h, k)) {
+      symbol_name s = kh_key(h, k);
+
+      if (!s.lit) {
+        mrb_free(mrb, (char*)s.name);
+      }
+    }
   kh_destroy(n2s, mrb, mrb->name2sym);
 }