random: Remove engine_combinedlcg.c (#15216)

The standalone engine cannot be usefully used for any other purpose. Remove it
and inline the implementation into the `php_combined_lcg()` function.

Author: TimWolla

UPGRADING.INTERNALS

@@ -277,6 +277,10 @@ PHP 8.4 INTERNALS UPGRADE NOTES
      implementation has been improved to generate better seeds, however any
      users should use the opportunity to verify that seeding is first
      attempted using the CSPRNG for better output size flexibility.
+   - The standalone combined_lcg engine has been removed, as the lcg_value()
+     userland function is deprecated and as the engine is unable to return
+     unbiased integer values. The internal php_combined_lcg() function remains
+     available for now.
 
  c. ext/xsl
    - The function php_xsl_create_object() was removed as it was not used

ext/random/config.m4

@@ -17,7 +17,6 @@ dnl Setup extension
 dnl
 PHP_NEW_EXTENSION([random], m4_normalize([
     csprng.c
-    engine_combinedlcg.c
     engine_mt19937.c
     engine_pcgoneseq128xslrr64.c
     engine_secure.c

ext/random/config.w32

@@ -1,4 +1,4 @@
 EXTENSION("random", "random.c", false /* never shared */, "/DZEND_ENABLE_STATIC_TSRMLS_CACHE=1");
 PHP_RANDOM="yes";
-ADD_SOURCES(configure_module_dirname, "csprng.c engine_combinedlcg.c engine_mt19937.c engine_pcgoneseq128xslrr64.c engine_xoshiro256starstar.c engine_secure.c engine_user.c gammasection.c randomizer.c zend_utils.c", "random");
+ADD_SOURCES(configure_module_dirname, "csprng.c engine_mt19937.c engine_pcgoneseq128xslrr64.c engine_xoshiro256starstar.c engine_secure.c engine_user.c gammasection.c randomizer.c zend_utils.c", "random");
 PHP_INSTALL_HEADERS("ext/random", "php_random.h php_random_csprng.h php_random_uint128.h");

ext/random/engine_combinedlcg.c

@@ -61,10 +61,6 @@ PHPAPI uint32_t php_mt_rand(void);
 PHPAPI zend_long php_mt_rand_range(zend_long min, zend_long max);
 PHPAPI zend_long php_mt_rand_common(zend_long min, zend_long max);
 
-typedef struct _php_random_status_state_combinedlcg {
-	int32_t state[2];
-} php_random_status_state_combinedlcg;
-
 typedef struct _php_random_status_state_mt19937 {
 	uint32_t count;
 	enum php_random_mt19937_mode mode;
@@ -107,7 +103,6 @@ typedef struct _php_random_fallback_seed_state {
 	unsigned char seed[20];
 } php_random_fallback_seed_state;
 
-extern PHPAPI const php_random_algo php_random_algo_combinedlcg;
 extern PHPAPI const php_random_algo php_random_algo_mt19937;
 extern PHPAPI const php_random_algo php_random_algo_pcgoneseq128xslrr64;
 extern PHPAPI const php_random_algo php_random_algo_xoshiro256starstar;
@@ -176,9 +171,6 @@ static inline php_random_algo_with_state php_random_default_engine(void)
 PHPAPI zend_string *php_random_bin2hex_le(const void *ptr, const size_t len);
 PHPAPI bool php_random_hex2bin_le(zend_string *hexstr, void *dest);
 
-PHPAPI void php_random_combinedlcg_seed64(php_random_status_state_combinedlcg *state, uint64_t seed);
-PHPAPI void php_random_combinedlcg_seed_default(php_random_status_state_combinedlcg *state);
-
 PHPAPI void php_random_mt19937_seed32(php_random_status_state_mt19937 *state, uint32_t seed);
 PHPAPI void php_random_mt19937_seed_default(php_random_status_state_mt19937 *state);
 
@@ -206,7 +198,7 @@ ZEND_BEGIN_MODULE_GLOBALS(random)
 	bool combined_lcg_seeded;
 	bool mt19937_seeded;
 	php_random_fallback_seed_state fallback_seed_state;
-	php_random_status_state_combinedlcg combined_lcg;
+	int32_t combined_lcg[2];
 	php_random_status_state_mt19937 mt19937;
 ZEND_END_MODULE_GLOBALS(random)
 

ext/random/php_random.h

@@ -396,14 +396,44 @@ PHPAPI bool php_random_hex2bin_le(zend_string *hexstr, void *dest)
 /* {{{ php_combined_lcg */
 PHPAPI double php_combined_lcg(void)
 {
-	php_random_status_state_combinedlcg *state = &RANDOM_G(combined_lcg);
+	int32_t *state = RANDOM_G(combined_lcg);
 
 	if (!RANDOM_G(combined_lcg_seeded)) {
-		php_random_combinedlcg_seed_default(state);
+		uint64_t seed = 0;
+
+		if (php_random_bytes_silent(&seed, sizeof(seed)) == FAILURE) {
+			seed = php_random_generate_fallback_seed();
+		}
+
+		state[0] = seed & 0xffffffffU;
+		state[1] = seed >> 32;
 		RANDOM_G(combined_lcg_seeded) = true;
 	}
 
-	return php_random_algo_combinedlcg.generate(state).result * 4.656613e-10;
+	/*
+	 * combinedLCG() returns a pseudo random number in the range of (0, 1).
+	 * The function combines two CGs with periods of
+	 * 2^31 - 85 - 1 and 2^31 - 249 - 1. The period of this function
+	 * is equal to the product of the two underlying periods, divided
+	 * by factors shared by the underlying periods, i.e. 2.3 * 10^18.
+	 *
+	 * see: https://library.sciencemadness.org/lanl1_a/lib-www/numerica/f7-1.pdf
+	 */
+#define PHP_COMBINED_LCG_MODMULT(a, b, c, m, s) q = s / a; s = b * (s - a * q) - c * q; if (s < 0) s += m
+
+	int32_t q, z;
+
+	/* state[0] = (state[0] * 40014) % 2147483563; */
+	PHP_COMBINED_LCG_MODMULT(53668, 40014, 12211, 2147483563L, state[0]);
+	/* state[1] = (state[1] * 40692) % 2147483399; */
+	PHP_COMBINED_LCG_MODMULT(52774, 40692, 3791, 2147483399L, state[1]);
+
+	z = state[0] - state[1];
+	if (z < 1) {
+		z += 2147483562;
+	}
+
+	return ((uint64_t)z) * 4.656613e-10;
 }
 /* }}} */