Replace Gravitron RNG with seeded Xoshiro

This is to make it so RNG is deterministic when played back with the
same inputs in a libTAS movie even if screen effects or backgrounds are
disabled.

That way, Gravitron RNG is on its own system (seeded in hardreset()),
separate from the constant fRandom() calls that go to visual systems and
don't do anything of actual consequence.

The seed is based off of SDL_GetTicks(), so RTA runners don't get the
same Gravitron RNG every time. This also paves the way for a future
in-built input-based recording system, which now only has to save the
seed for a given recording in order for it to play back
deterministically.

desktop_version/CMakeLists.txt

@@ -112,6 +112,7 @@ set(VVV_SRC
 	src/GlitchrunnerMode.c
 	src/Network.c
 	src/ThirdPartyDeps.c
+	src/Xoshiro.c
 )
 if(NOT CUSTOM_LEVEL_SUPPORT STREQUAL "DISABLED")
 	list(APPEND VVV_SRC src/editor.cpp)

desktop_version/src/Entity.cpp

@@ -11,6 +11,7 @@
 #include "Music.h"
 #include "Script.h"
 #include "UtilityClass.h"
+#include "Xoshiro.h"
 
 bool entityclass::checktowerspikes(int t)
 {
@@ -210,7 +211,7 @@ void entityclass::generateswnwave( int t )
                 if (game.deathcounts - game.swndeaths > 25) game.swndelay += 4;
                 break;
             case 1:
-                createentity(-150, 58 + (int(fRandom() * 6) * 20), 23, 0, 0);
+                createentity(-150, 58 + (int(xoshiro_rand() * 6) * 20), 23, 0, 0);
                 game.swnstate = 0;
                 game.swndelay = 0; //return to decision state
                 break;
@@ -238,13 +239,13 @@ void entityclass::generateswnwave( int t )
                 game.swndelay = 0; //return to decision state
                 break;
             case 3:
-                createentity(320+150, 58 + (int(fRandom() * 6) * 20), 23, 1, 0);
+                createentity(320+150, 58 + (int(xoshiro_rand() * 6) * 20), 23, 1, 0);
                 game.swnstate = 0;
                 game.swndelay = 0; //return to decision state
                 break;
             case 4:
                 //left and right compliments
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 createentity(-150, 58 + (game.swnstate2  * 20), 23, 0, 0);
                 createentity(320+150, 58 + ((5-game.swnstate2) * 20), 23, 1, 0);
                 game.swnstate = 0;
@@ -319,7 +320,7 @@ void entityclass::generateswnwave( int t )
                 game.swnstate3 = 0;
                 game.swnstate4 = 0;
 
-                game.swnstate2 = int(fRandom() * 100);
+                game.swnstate2 = int(xoshiro_rand() * 100);
                 if (game.swnstate2 < 25)
                 {
                     //simple
@@ -336,7 +337,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 1:
                 //complex chain
-                game.swnstate2 = int(fRandom() * 8);
+                game.swnstate2 = int(xoshiro_rand() * 8);
                 if (game.swnstate2 == 0)
                 {
                     game.swnstate = 10;
@@ -382,7 +383,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 2:
                 //simple chain
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 if (game.swnstate2 == 0)
                 {
                     game.swnstate = 23;
@@ -418,7 +419,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 3:
                 //Choose a major action
-                game.swnstate2 = int(fRandom() * 100);
+                game.swnstate2 = int(xoshiro_rand() * 100);
                 game.swnstate4 = 0;
                 if (game.swnstate2 < 25)
                 {
@@ -435,7 +436,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 4:
                 //filler chain
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 if (game.swnstate2 == 0)
                 {
                     game.swnstate = 28;
@@ -624,7 +625,7 @@ void entityclass::generateswnwave( int t )
             case 22:
                 game.swnstate4++;
                 //left and right compliments
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 createentity(-150, 58 + (game.swnstate2  * 20), 23, 0, 0);
                 createentity(320 + 150, 58 + ((5 - game.swnstate2) * 20), 23, 1, 0);
                 if(game.swnstate4<=12)
@@ -685,7 +686,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 28:
                 game.swnstate4++;
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 createentity(-150, 58 + (game.swnstate2  * 20), 23, 0, 0);
                 if(game.swnstate4<=6)
                 {
@@ -701,7 +702,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 29:
                 game.swnstate4++;
-                game.swnstate2 = int(fRandom() * 6);
+                game.swnstate2 = int(xoshiro_rand() * 6);
                 gravcreate(game.swnstate2, 1);
                 if(game.swnstate4<=6)
                 {
@@ -717,7 +718,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 30:
                 game.swnstate4++;
-                game.swnstate2 = int(fRandom() * 3);
+                game.swnstate2 = int(xoshiro_rand() * 3);
                 gravcreate(game.swnstate2, 0);
                 gravcreate(5-game.swnstate2, 0);
                 if(game.swnstate4<=2)
@@ -734,7 +735,7 @@ void entityclass::generateswnwave( int t )
                 break;
             case 31:
                 game.swnstate4++;
-                game.swnstate2 = int(fRandom() * 3);
+                game.swnstate2 = int(xoshiro_rand() * 3);
                 gravcreate(game.swnstate2, 1);
                 gravcreate(5-game.swnstate2, 1);
                 if(game.swnstate4<=2)

desktop_version/src/Script.cpp

@@ -2,6 +2,7 @@
 #include "Script.h"
 
 #include <limits.h>
+#include <SDL_timer.h>
 
 #include "editor.h"
 #include "Entity.h"
@@ -13,6 +14,7 @@
 #include "Map.h"
 #include "Music.h"
 #include "UtilityClass.h"
+#include "Xoshiro.h"
 
 scriptclass::scriptclass(void)
 {
@@ -3377,6 +3379,8 @@ void scriptclass::hardreset(void)
 {
 	const bool version2_2 = GlitchrunnerMode_less_than_or_equal(Glitchrunner2_2);
 
+	xoshiro_seed(SDL_GetTicks());
+
 	//Game:
 	game.hascontrol = true;
 	game.gravitycontrol = 0;

desktop_version/src/Xoshiro.c

@@ -0,0 +1,62 @@
+#include <stdint.h>
+
+/* Implements the xoshiro128+ PRNG. */
+
+static uint32_t rotl(const uint32_t x, const int k)
+{
+    return (x << k) | (x >> (32 - k));
+}
+
+static uint32_t s[4];
+
+static uint32_t splitmix32(uint32_t* x)
+{
+    uint32_t z = (*x += 0x9e3779b9UL);
+    z = (z ^ (z >> 15)) * 0xbf58476dUL;
+    z = (z ^ (z >> 13)) * 0x94d049bbUL;
+    return z ^ (z >> 16);
+}
+
+static void seed(
+    const uint32_t s0,
+    const uint32_t s1,
+    const uint32_t s2,
+    const uint32_t s3
+) {
+    s[0] = s0;
+    s[1] = s1;
+    s[2] = s2;
+    s[3] = s3;
+}
+
+uint32_t xoshiro_next(void)
+{
+    const uint32_t result = s[0] + s[3];
+
+    const uint32_t t = s[1] << 9;
+
+    s[2] ^= s[0];
+    s[3] ^= s[1];
+    s[1] ^= s[2];
+    s[0] ^= s[3];
+
+    s[2] ^= t;
+
+    s[3] = rotl(s[3], 11);
+
+    return result;
+}
+
+void xoshiro_seed(uint32_t s)
+{
+    const uint32_t s0 = splitmix32(&s);
+    const uint32_t s1 = splitmix32(&s);
+    const uint32_t s2 = splitmix32(&s);
+    const uint32_t s3 = splitmix32(&s);
+    seed(s0, s1, s2, s3);
+}
+
+float xoshiro_rand(void)
+{
+    return ((float) xoshiro_next()) / ((float) UINT32_MAX);
+}

desktop_version/src/Xoshiro.h

@@ -0,0 +1,21 @@
+#ifndef XOSHIRO_H
+#define XOSHIRO_H
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include <stdint.h>
+
+void xoshiro_seed(uint32_t s);
+
+uint32_t xoshiro_next(void);
+
+float xoshiro_rand(void);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* XOSHIRO_H */