'math.randomseed()' sets a somewhat random seed
When called with no arguments, 'math.randomseed' uses time and ASLR
to generate a somewhat random seed. the initial seed when Lua starts
is generated this way.
diff --git a/lmathlib.c b/lmathlib.c
index f2bfff9..e3ccc3e 100644
--- a/lmathlib.c
+++ b/lmathlib.c
@@ -301,7 +301,7 @@
/* rotate left 'x' by 'n' bits */
static Rand64 rotl (Rand64 x, int n) {
- return (x << n) | (trim64(x) >> (64 - n));
+ return (x << n) | (trim64(x) >> (64 - n));
}
static Rand64 nextrand (Rand64 *state) {
@@ -597,11 +597,27 @@
}
+/*
+** Set a "random" seed. To get some randomness, use the current time
+** and the address of 'L' (in case the machine does address space layout
+** randomization).
+*/
+static void randseed (lua_State *L, RanState *state) {
+ lua_Unsigned seed1 = (lua_Unsigned)time(NULL);
+ lua_Unsigned seed2 = (lua_Unsigned)(size_t)L;
+ setseed(state->s, seed1, seed2);
+}
+
+
static int math_randomseed (lua_State *L) {
RanState *state = (RanState *)lua_touserdata(L, lua_upvalueindex(1));
- lua_Integer n1 = luaL_checkinteger(L, 1);
- lua_Integer n2 = luaL_optinteger(L, 2, 0);
- setseed(state->s, n1, n2);
+ if (lua_isnone(L, 1))
+ randseed(L, state);
+ else {
+ lua_Integer n1 = luaL_checkinteger(L, 1);
+ lua_Integer n2 = luaL_optinteger(L, 2, 0);
+ setseed(state->s, n1, n2);
+ }
return 0;
}
@@ -615,15 +631,10 @@
/*
** Register the random functions and initialize their state.
-** To give some "randomness" to the initial seed, use the current time
-** and the address of 'L' (in case the machine does address space layout
-** randomization).
*/
static void setrandfunc (lua_State *L) {
RanState *state = (RanState *)lua_newuserdatauv(L, sizeof(RanState), 0);
- lua_Unsigned seed1 = (lua_Unsigned)time(NULL);
- lua_Unsigned seed2 = (lua_Unsigned)(size_t)L;
- setseed(state->s, seed1, seed2);
+ randseed(L, state); /* initialize with a "random" seed */
luaL_setfuncs(L, randfuncs, 1);
}
diff --git a/manual/manual.of b/manual/manual.of
index 2eb8773..b47fd86 100644
--- a/manual/manual.of
+++ b/manual/manual.of
@@ -7643,14 +7643,10 @@
The call @T{math.random(0)} produces an integer with
all bits (pseudo)random.
-Lua initializes its pseudo-random generator with
-a weak attempt for ``randomness'',
+Lua initializes its pseudo-random generator with the equivalent of
+a call to @Lid{math.randomseed} with no arguments,
so that @id{math.random} should generate
different sequences of results each time the program runs.
-To ensure a required level of randomness to the initial state
-(or contrarily, to have a deterministic sequence,
-for instance when debugging a program),
-you should call @Lid{math.randomseed} explicitly.
The results from this function have good statistical qualities,
but they are not cryptographically secure.
@@ -7660,14 +7656,23 @@
}
-@LibEntry{math.randomseed (x [, y])|
+@LibEntry{math.randomseed ([x [, y]])|
-The integer parameters @id{x} and @id{y} are
-concatenated into a 128-bit @Q{seed} that
+When called with at least one argument,
+the integer parameters @id{x} and @id{y} are
+concatenated into a 128-bit @emphx{seed} that
is used to reinitialize the pseudo-random generator;
equal seeds produce equal sequences of numbers.
The default for @id{y} is zero.
+When called with no arguments,
+Lua generates a seed with
+a weak attempt for randomness.
+To ensure a required level of randomness to the initial state
+(or contrarily, to have a deterministic sequence,
+for instance when debugging a program),
+you should call @Lid{math.randomseed} with explicit arguments.
+
}
@LibEntry{math.sin (x)|
diff --git a/testes/math.lua b/testes/math.lua
index dc5b84f..b010ff6 100644
--- a/testes/math.lua
+++ b/testes/math.lua
@@ -838,7 +838,7 @@
assert(rand * 2^floatbits == res)
end
-math.randomseed(0, os.time())
+math.randomseed()
do -- test random for floats
local randbits = math.min(floatbits, 64) -- at most 64 random bits
