LibJS/AK: Move XorShift128PlusRNG to AK

This will be useful for CSS random functions so it should be in a
reusable place.

This does require us to use `AK::get_random` instead of
`Crypto::get_secure_random`, but this is fine since the latter is in the
process of being removed (see #6564).

AK/Random.cpp

@@ -97,4 +97,41 @@ u64 get_random_uniform_64(u64 max_bounds)
     return random_value % max_bounds;
 }
 
+XorShift128PlusRNG::XorShift128PlusRNG()
+{
+    // Splitmix64 is used as xorshift is sensitive to being seeded with all 0s
+    u64 seed = get_random<u64>();
+    m_low = splitmix64(seed);
+    seed = get_random<u64>();
+    m_high = splitmix64(seed);
+}
+
+double XorShift128PlusRNG::get()
+{
+    u64 value = advance() & ((1ULL << 53) - 1);
+    return value * (1.0 / (1ULL << 53));
+}
+
+u64 XorShift128PlusRNG::splitmix64(u64& state)
+{
+    u64 z = (state += 0x9e3779b97f4a7c15ULL);
+    z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ULL;
+    z = (z ^ (z >> 27)) * 0x94d049bb133111ebULL;
+    return z ^ (z >> 31);
+}
+
+// Apparently this set of constants is better: https://stackoverflow.com/a/34432126
+u64 XorShift128PlusRNG::advance()
+{
+    u64 s1 = m_low;
+    u64 const s0 = m_high;
+    u64 const result = s0 + s1;
+    m_low = s0;
+    s1 ^= s1 << 23;
+    s1 ^= s1 >> 18;
+    s1 ^= s0 ^ (s0 >> 5);
+    m_high = s1;
+    return result + s1;
+}
+
 }

AK/Random.h

@@ -31,6 +31,19 @@ inline T get_random()
 u32 get_random_uniform(u32 max_bounds);
 u64 get_random_uniform_64(u64 max_bounds);
 
+// http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
+class XorShift128PlusRNG {
+public:
+    XorShift128PlusRNG();
+    double get();
+
+private:
+    u64 splitmix64(u64& state);
+    u64 advance();
+    u64 m_low { 0 };
+    u64 m_high { 0 };
+};
+
 template<typename Collection>
 inline void shuffle(Collection& collection)
 {
@@ -48,4 +61,5 @@ using AK::fill_with_random;
 using AK::get_random;
 using AK::get_random_uniform;
 using AK::shuffle;
+using AK::XorShift128PlusRNG;
 #endif

Libraries/LibJS/Runtime/MathObject.cpp

@@ -809,51 +809,6 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::pow)
     return pow_impl(vm, vm.argument(0), vm.argument(1));
 }
 
-// http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
-class XorShift128PlusRNG {
-public:
-    XorShift128PlusRNG()
-    {
-        // Splitmix64 is used as xorshift is sensitive to being seeded with all 0s
-        u64 seed = Crypto::get_secure_random<u64>();
-        m_low = splitmix64(seed);
-        seed = Crypto::get_secure_random<u64>();
-        m_high = splitmix64(seed);
-    }
-
-    double get()
-    {
-        u64 value = advance() & ((1ULL << 53) - 1);
-        return value * (1.0 / (1ULL << 53));
-    }
-
-private:
-    u64 splitmix64(u64& state)
-    {
-        u64 z = (state += 0x9e3779b97f4a7c15ULL);
-        z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ULL;
-        z = (z ^ (z >> 27)) * 0x94d049bb133111ebULL;
-        return z ^ (z >> 31);
-    }
-
-    // Apparently this set of constants is better: https://stackoverflow.com/a/34432126
-    u64 advance()
-    {
-        u64 s1 = m_low;
-        u64 const s0 = m_high;
-        u64 const result = s0 + s1;
-        m_low = s0;
-        s1 ^= s1 << 23;
-        s1 ^= s1 >> 18;
-        s1 ^= s0 ^ (s0 >> 5);
-        m_high = s1;
-        return result + s1;
-    }
-
-    u64 m_low { 0 };
-    u64 m_high { 0 };
-};
-
 Value MathObject::random_impl()
 {
     // This function returns a Number value with positive sign, greater than or equal to +0𝔽 but strictly less than 1𝔽,