Move random number generator from Math.random to jerry-libc, replace the logic with call to rand in Math.random.

JerryScript-DCO-1.0-Signed-off-by: Ruben Ayrapetyan [email protected]

Author: ruben-ayrapetyan

jerry-core/ecma/builtin-objects/ecma-builtin-math.cpp

@@ -25,8 +25,9 @@
 #include "ecma-objects.h"
 #include "ecma-objects-general.h"
 #include "ecma-try-catch-macro.h"
-#include "jrt.h"
 #include "fdlibm-math.h"
+#include "jrt.h"
+#include "jrt-libc-includes.h"
 
 #ifndef CONFIG_ECMA_COMPACT_PROFILE_DISABLE_MATH_BUILTIN
 
@@ -528,26 +529,24 @@ ecma_builtin_math_object_pow (ecma_value_t this_arg __attr_unused___, /**< 'this
 static ecma_completion_value_t
 ecma_builtin_math_object_random (ecma_value_t this_arg __attr_unused___) /**< 'this' argument */
 {
-  /* Implementation of George Marsaglia's XorShift random number generator */
-  TODO (/* Check for license issues */);
-
-  static uint32_t word1 = 1455997910;
-  static uint32_t word2 = 1999515274;
-  static uint32_t word3 = 1234451287;
-  static uint32_t word4 = 1949149569;
-
-  uint32_t intermediate = word1 ^ (word1 << 11);
-  intermediate ^= intermediate >> 8;
-
-  word1 = word2;
-  word2 = word3;
-  word3 = word4;
-
-  word4 ^= word4 >> 19;
-  word4 ^= intermediate;
+  uint32_t rnd = 1;
+  uint32_t reps_count;
+#if RAND_MAX < 0x100
+  reps_count = 4;
+#elif RAND_MAX < 0x10000
+  reps_count = 2;
+#else /* RAND_MAX < 0x10000 */
+  reps_count = 1;
+#endif /* RAND_MAX >= 0x10000 */
+
+  for (uint32_t i = 0; i < reps_count; i++)
+  {
+    uint32_t next_rand = (uint32_t) rand ();
+    rnd *= next_rand;
+  }
 
   const uint32_t max_uint32 = (uint32_t) -1;
-  ecma_number_t rand = (ecma_number_t) word4;
+  ecma_number_t rand = (ecma_number_t) rnd;
   rand /= (ecma_number_t) max_uint32;
   rand *= (ecma_number_t) (max_uint32 - 1) / (ecma_number_t) max_uint32;
 

jerry-libc/include/stdlib.h

@@ -25,4 +25,15 @@
 extern EXTERN_C void __attribute__ ((noreturn)) exit (int);
 extern EXTERN_C void __attribute__ ((noreturn)) abort (void);
 
+/**
+ * Maximum integer that could be returned by random number generator
+ *
+ * See also:
+ *          rand
+ */
+#define RAND_MAX (0x7fffffffu)
+
+extern EXTERN_C int rand (void);
+extern EXTERN_C void srand (unsigned int);
+
 #endif /* !JERRY_LIBC_STDLIB_H */

jerry-libc/jerry-libc.c

@@ -24,6 +24,11 @@
 
 #include "jerry-libc-defs.h"
 
+/**
+ * State of pseudo-random number generator
+ */
+static unsigned int libc_random_gen_state[4] = { 1455997910, 1999515274, 1234451287, 1949149569 };
+
 /**
  * Standard file descriptors
  */
@@ -326,3 +331,38 @@ isxdigit (int c)
 {
   return isdigit (c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
 }
+
+/**
+ * Generate pseudo-random integer
+ *
+ * Note:
+ *      The function implements George Marsaglia's XorShift random number generator
+ *
+ * @return integer in range [0; RAND_MAX]
+ */
+int
+rand (void)
+{
+  uint32_t intermediate = libc_random_gen_state[0] ^ (libc_random_gen_state[0] << 11);
+  intermediate ^= intermediate >> 8;
+
+  libc_random_gen_state[0] = libc_random_gen_state[1];
+  libc_random_gen_state[1] = libc_random_gen_state[2];
+  libc_random_gen_state[2] = libc_random_gen_state[3];
+
+  libc_random_gen_state[3] ^= libc_random_gen_state[3] >> 19;
+  libc_random_gen_state[3] ^= intermediate;
+
+  uint32_t ret = libc_random_gen_state[3] % (RAND_MAX + 1u);
+
+  return (int32_t) ret;
+} /* rand */
+
+/**
+ * Initialize pseudo-random number generator with the specified seed value
+ */
+void
+srand (unsigned int seed) /**< new seed */
+{
+  libc_random_gen_state[3] = seed;
+} /* srand */