[Bug #19100] Add init_int32 function to rb_random_interface_t

Distinguish initialization by single word from initialization by
array.

ext/-test-/random/bad_version.c

@@ -20,6 +20,9 @@ bad_version_init(rb_random_t *rnd, const uint32_t *buf, size_t len)
     must_not_reach();
 }
 
+NORETURN(static void bad_version_init_int32(rb_random_t *, uint32_t));
+RB_RANDOM_DEFINE_INIT_INT32_FUNC(bad_version)
+
 NORETURN(static void bad_version_get_bytes(rb_random_t *, void *, size_t));
 static void
 bad_version_get_bytes(rb_random_t *rnd, void *p, size_t n)

ext/-test-/random/loop.c

@@ -13,6 +13,7 @@ static const rb_random_interface_t random_loop_if = {
     RB_RANDOM_INTERFACE_DEFINE_WITH_REAL(loop)
 };
 
+RB_RANDOM_DEFINE_INIT_INT32_FUNC(loop);
 static size_t
 random_loop_memsize(const void *ptr)
 {

include/ruby/random.h

@@ -19,7 +19,7 @@
 /*
  * version
  * 0: before versioning; deprecated
- * 1: added version and flags
+ * 1: added version, flags and init_32bit function
  */
 #define RUBY_RANDOM_INTERFACE_VERSION_MAJOR 1
 #define RUBY_RANDOM_INTERFACE_VERSION_MINOR 0
@@ -66,6 +66,17 @@ RBIMPL_ATTR_NONNULL(())
  */
 typedef void rb_random_init_func(rb_random_t *rng, const uint32_t *buf, size_t len);
 
+RBIMPL_ATTR_NONNULL(())
+/**
+ * This is the type of functions called when your random object is initialised.
+ * Passed data is the seed integer.
+ *
+ * @param[out]  rng  Your random struct to fill in.
+ * @param[in]   data Seed, single word.
+ * @post        `rng` is initialised using the passed seeds.
+ */
+typedef void rb_random_init_int32_func(rb_random_t *rng, uint32_t data);
+
 RBIMPL_ATTR_NONNULL(())
 /**
  * This is the type of functions  called from your object's `#rand` method.
@@ -116,9 +127,12 @@ typedef struct {
      */
     uint16_t flags;
 
-    /** Initialiser function. */
+    /** Function to initialize from uint32_t array. */
     rb_random_init_func *init;
 
+    /** Function to initialize from single uint32_t. */
+    rb_random_init_int32_func *init_int32;
+
     /** Function to obtain a random integer. */
     rb_random_get_int32_func *get_int32;
 
@@ -162,11 +176,12 @@ typedef struct {
 } rb_random_interface_t;
 
 /**
- * This utility macro defines  3 functions named prefix_init, prefix_get_int32,
- * prefix_get_bytes.
+ * This utility macro defines 4 functions named prefix_init, prefix_init_int32,
+ * prefix_get_int32, prefix_get_bytes.
  */
 #define RB_RANDOM_INTERFACE_DECLARE(prefix) \
     static void prefix##_init(rb_random_t *, const uint32_t *, size_t); \
+    static void prefix##_init_int32(rb_random_t *, uint32_t); \
     static unsigned int prefix##_get_int32(rb_random_t *); \
     static void prefix##_get_bytes(rb_random_t *, void *, size_t)
 
@@ -195,6 +210,7 @@ typedef struct {
 #define RB_RANDOM_INTERFACE_DEFINE(prefix) \
     RUBY_RANDOM_INTERFACE_VERSION_INITIALIZER, 0, \
     prefix##_init, \
+    prefix##_init_int32, \
     prefix##_get_int32, \
     prefix##_get_bytes
 
@@ -206,6 +222,12 @@ typedef struct {
     RB_RANDOM_INTERFACE_DEFINE(prefix), \
     prefix##_get_real
 
+#define RB_RANDOM_DEFINE_INIT_INT32_FUNC(prefix) \
+    static void prefix##_init_int32(rb_random_t *rnd, uint32_t data) \
+    { \
+        prefix##_init(rnd, &data, 1); \
+    }
+
 #if defined _WIN32 && !defined __CYGWIN__
 typedef rb_data_type_t rb_random_data_type_t;
 # define RB_RANDOM_PARENT 0

random.c

@@ -371,11 +371,14 @@ rand_init(const rb_random_interface_t *rng, rb_random_t *rnd, VALUE seed)
         INTEGER_PACK_LSWORD_FIRST|INTEGER_PACK_NATIVE_BYTE_ORDER);
     if (sign < 0)
         sign = -sign;
-    if (len > 1) {
+    if (len <= 1) {
+        rng->init_int32(rnd, len ? buf[0] : 0);
+    }
+    else {
         if (sign != 2 && buf[len-1] == 1) /* remove leading-zero-guard */
             len--;
+        rng->init(rnd, buf, len);
     }
-    rng->init(rnd, buf, len);
     explicit_bzero(buf, len * sizeof(*buf));
     ALLOCV_END(buf0);
     return seed;
@@ -891,16 +894,18 @@ rand_mt_load(VALUE obj, VALUE dump)
     return obj;
 }
 
+static void
+rand_mt_init_int32(rb_random_t *rnd, uint32_t data)
+{
+    struct MT *mt = &((rb_random_mt_t *)rnd)->mt;
+    init_genrand(mt, data);
+}
+
 static void
 rand_mt_init(rb_random_t *rnd, const uint32_t *buf, size_t len)
 {
     struct MT *mt = &((rb_random_mt_t *)rnd)->mt;
-    if (len <= 1) {
-        init_genrand(mt, len ? buf[0] : 0);
-    }
-    else {
-        init_by_array(mt, buf, (int)len);
-    }
+    init_by_array(mt, buf, (int)len);
 }
 
 static unsigned int

test/ruby/test_rand.rb

@@ -336,6 +336,14 @@ def test_seed
     }
   end
 
+  def test_seed_leading_zero_guard
+    guard = 1<<32
+    range = 0...(1<<32)
+    all_assertions_foreach(nil, 0, 1, 2) do |i|
+      assert_not_equal(Random.new(i).rand(range), Random.new(i+guard).rand(range))
+    end
+  end
+
   def test_marshal
     bug3656 = '[ruby-core:31622]'
     assert_raise(TypeError, bug3656) {