Use `MRB_TT_ISTRUCT` for `Random` to reduce memory.

When the size of Xorshift128 seed (`sizeof(uint32)*4`) is bigger than
ISTRUCT_DATA_SIZE, `Random` uses Xorshift96 instead.

mrbgems/mruby-random/src/random.c

@@ -9,17 +9,19 @@
 #include <mruby/class.h>
 #include <mruby/data.h>
 #include <mruby/array.h>
+#include <mruby/istruct.h>
+#if INT32_MAX <= INTPTR_MAX
+# define XORSHIFT96
+# define NSEEDS 3
+#else
+# define NSEEDS 4
+#endif
+#define LASTSEED (NSEEDS-1)
 
 #include <time.h>
 
-static char const RAND_STATE_KEY[] = "$mrb_i_rand_state";
-
-static const struct mrb_data_type rand_state_type = {
-  RAND_STATE_KEY, mrb_free,
-};
-
 typedef struct rand_state {
-  uint32_t seed[4];
+  uint32_t seed[NSEEDS];
 } rand_state;
 
 static void
@@ -28,18 +30,39 @@ rand_init(rand_state *t)
   t->seed[0] = 123456789;
   t->seed[1] = 362436069;
   t->seed[2] = 521288629;
+#ifndef XORSHIFT96
   t->seed[3] = 88675123;
+#endif
 }
 
 static uint32_t
 rand_seed(rand_state *t, uint32_t seed)
 {
-  uint32_t old_seed = t->seed[3];
+  uint32_t old_seed = t->seed[LASTSEED];
   rand_init(t);
-  t->seed[3] = seed;
+  t->seed[LASTSEED] = seed;
   return old_seed;
 }
 
+#ifdef XORSHIFT96
+static uint32_t
+rand_uint32(rand_state *state)
+{
+  uint32_t *seed = state->seed;
+  uint32_t x = seed[0];
+  uint32_t y = seed[1];
+  uint32_t z = seed[2];
+  uint32_t t;
+
+  t = (x ^ (x << 3)) ^ (y ^ (y >> 19)) ^ (z ^ (z << 6));
+  x = y; y = z; z = t;
+  seed[0] = x;
+  seed[1] = y;
+  seed[2] = z;
+
+  return z;
+}
+#else  /* XORSHIFT96 */
 static uint32_t
 rand_uint32(rand_state *state)
 {
@@ -60,6 +83,7 @@ rand_uint32(rand_state *state)
 
   return w;
 }
+#endif  /* XORSHIFT96 */
 
 #ifndef MRB_WITHOUT_FLOAT
 static double
@@ -109,19 +133,26 @@ get_opt(mrb_state* mrb)
   return arg;
 }
 
+static void
+random_check(mrb_state *mrb, mrb_value random) {
+  struct RClass *c = mrb_class_get(mrb, "Random");
+  if (!mrb_obj_is_kind_of(mrb, random, c) || mrb_type(random) != MRB_TT_ISTRUCT) {
+    mrb_raise(mrb, E_TYPE_ERROR, "Random instance required");
+  }
+}
+
 static mrb_value
 random_default(mrb_state *mrb) {
-  return mrb_const_get(mrb,
-             mrb_obj_value(mrb_class_get(mrb, "Random")),
-             mrb_intern_lit(mrb, "DEFAULT"));
+  struct RClass *c = mrb_class_get(mrb, "Random");
+  mrb_value d = mrb_const_get(mrb, mrb_obj_value(c), mrb_intern_lit(mrb, "DEFAULT"));
+  if (!mrb_obj_is_kind_of(mrb, d, c)) {
+    mrb_raise(mrb, E_TYPE_ERROR, "Random::DEFAULT replaced");
+  }
+  return d;
 }
 
-static rand_state *
-random_state(mrb_state *mrb)
-{
-  mrb_value random_val = random_default(mrb);
-  return DATA_GET_PTR(mrb, random_val, &rand_state_type, rand_state);
-}
+#define random_ptr(v) (rand_state*)mrb_istruct_ptr(v)
+#define random_default_state(mrb) random_ptr(random_default(mrb))
 
 static mrb_value
 random_m_init(mrb_state *mrb, mrb_value self)
@@ -131,11 +162,7 @@ random_m_init(mrb_state *mrb, mrb_value self)
 
   seed = get_opt(mrb);
   /* avoid memory leaks */
-  t = (rand_state*)DATA_PTR(self);
-  if (t == NULL) {
-    t = (rand_state *)mrb_malloc(mrb, sizeof(rand_state));
-    mrb_data_init(self, t, &rand_state_type);
-  }
+  t = random_ptr(self);
   if (mrb_nil_p(seed)) {
     rand_init(t);
   }
@@ -150,7 +177,7 @@ static mrb_value
 random_m_rand(mrb_state *mrb, mrb_value self)
 {
   mrb_value max;
-  rand_state *t = DATA_GET_PTR(mrb, self, &rand_state_type, rand_state);
+  rand_state *t = random_ptr(self);
 
   max = get_opt(mrb);
   return random_rand(mrb, t, max);
@@ -162,7 +189,7 @@ random_m_srand(mrb_state *mrb, mrb_value self)
   uint32_t seed;
   uint32_t old_seed;
   mrb_value sv;
-  rand_state *t = DATA_GET_PTR(mrb, self, &rand_state_type, rand_state);
+  rand_state *t = random_ptr(self);
 
   sv = get_opt(mrb);
   if (mrb_nil_p(sv)) {
@@ -188,13 +215,18 @@ mrb_ary_shuffle_bang(mrb_state *mrb, mrb_value ary)
 {
   mrb_int i;
   mrb_value max;
-  rand_state *random = NULL;
+  mrb_value r = mrb_nil_value();
+  rand_state *random;
 
   if (RARRAY_LEN(ary) > 1) {
-    mrb_get_args(mrb, "|d", &random, &rand_state_type);
+    mrb_get_args(mrb, "|o", &r);
 
-    if (random == NULL) {
-      random = random_state(mrb);
+    if (mrb_nil_p(r)) {
+      random = random_default_state(mrb);
+    }
+    else {
+      random_check(mrb, r);
+      random = random_ptr(r);
     }
     mrb_ary_modify(mrb, mrb_ary_ptr(ary));
     max = mrb_fixnum_value(RARRAY_LEN(ary));
@@ -250,12 +282,17 @@ mrb_ary_sample(mrb_state *mrb, mrb_value ary)
 {
   mrb_int n = 0;
   mrb_bool given;
-  rand_state *random = NULL;
+  mrb_value r = mrb_nil_value();
+  rand_state *random;
   mrb_int len;
 
-  mrb_get_args(mrb, "|i?d", &n, &given, &random, &rand_state_type);
-  if (random == NULL) {
-    random = random_state(mrb);
+  mrb_get_args(mrb, "|i?o", &n, &given, &r);
+  if (mrb_nil_p(r)) {
+    random = random_default_state(mrb);
+  }
+  else {
+    random_check(mrb, r);
+    random = random_ptr(r);
   }
   len = RARRAY_LEN(ary);
   if (!given) {                 /* pick one element */
@@ -301,7 +338,7 @@ mrb_ary_sample(mrb_state *mrb, mrb_value ary)
 static mrb_value
 random_f_rand(mrb_state *mrb, mrb_value self)
 {
-  rand_state *t = random_state(mrb);
+  rand_state *t = random_default_state(mrb);
   return random_rand(mrb, t, get_opt(mrb));
 }
 
@@ -318,11 +355,13 @@ void mrb_mruby_random_gem_init(mrb_state *mrb)
   struct RClass *random;
   struct RClass *array = mrb->array_class;
 
+  mrb_assert(sizeof(rand_state) < ISTRUCT_DATA_SIZE);
+
   mrb_define_method(mrb, mrb->kernel_module, "rand", random_f_rand, MRB_ARGS_OPT(1));
   mrb_define_method(mrb, mrb->kernel_module, "srand", random_f_srand, MRB_ARGS_OPT(1));
 
   random = mrb_define_class(mrb, "Random", mrb->object_class);
-  MRB_SET_INSTANCE_TT(random, MRB_TT_DATA);
+  MRB_SET_INSTANCE_TT(random, MRB_TT_ISTRUCT);
   mrb_define_class_method(mrb, random, "rand", random_f_rand, MRB_ARGS_OPT(1));
   mrb_define_class_method(mrb, random, "srand", random_f_srand, MRB_ARGS_OPT(1));