Port to MT19337 PRNG.

Get rid of evil rand_byte(). Code still using rand() remains semi-broken
until the following commit.

inc/shared/shared.h

@@ -320,18 +320,6 @@ static inline float anglemod(float a)
     return a;
 }
 
-static inline int rand_byte(void)
-{
-    int r = rand();
-
-    int b1 = (r >> 24) & 255;
-    int b2 = (r >> 16) & 255;
-    int b3 = (r >>  8) & 255;
-    int b4 = (r) & 255;
-
-    return b1 ^ b2 ^ b3 ^ b4;
-}
-
 static inline int Q_align(int value, int align)
 {
     int mod = value % align;
@@ -348,6 +336,9 @@ static inline int Q_gcd(int a, int b)
     return a;
 }
 
+void Q_srand(uint32_t seed);
+uint32_t Q_rand(void);
+
 #define clamp(a,b,c)    ((a)<(b)?(a)=(b):(a)>(c)?(a)=(c):(a))
 #define cclamp(a,b,c)   ((b)>(c)?clamp(a,c,b):clamp(a,b,c))
 
@@ -359,8 +350,8 @@ static inline int Q_gcd(int a, int b)
 #define min(a,b) ((a)<(b)?(a):(b))
 #endif
 
-#define frand()     ((rand() & 32767) * (1.0f / 32767))
-#define crand()     ((rand() & 32767) * (2.0f / 32767) - 1)
+#define frand()     ((int32_t)Q_rand() * 0x1p-32f + 0.5f)
+#define crand()     ((int32_t)Q_rand() * 0x1p-31f)
 
 #define Q_rint(x)   ((x) < 0 ? ((int)((x) - 0.5f)) : ((int)((x) + 0.5f)))
 

src/baseq2/g_local.h

@@ -501,8 +501,8 @@ extern  edict_t         *g_edicts;
 #define GLOFS(x) q_offsetof(game_locals_t, x)
 #define CLOFS(x) q_offsetof(gclient_t, x)
 
-#define random()    ((rand () & 0x7fff) / ((float)0x7fff))
-#define crandom()   (2.0f * (random() - 0.5f))
+#define random()    frand()
+#define crandom()   crand()
 
 extern  cvar_t  *maxentities;
 extern  cvar_t  *deathmatch;

src/baseq2/g_main.c

@@ -115,6 +115,8 @@ void InitGame(void)
 {
     gi.dprintf("==== InitGame ====\n");
 
+    Q_srand(time(NULL));
+
     gun_x = gi.cvar("gun_x", "0", 0);
     gun_y = gi.cvar("gun_y", "0", 0);
     gun_z = gi.cvar("gun_z", "0", 0);

src/common/common.c

@@ -665,7 +665,7 @@ size_t Com_UptimeLong_m(char *buffer, size_t size)
 
 static size_t Com_Random_m(char *buffer, size_t size)
 {
-    return Q_scnprintf(buffer, size, "%d", rand_byte() % 10);
+    return Q_scnprintf(buffer, size, "%d", Q_rand() % 10);
 }
 
 static size_t Com_MapList_m(char *buffer, size_t size)
@@ -894,7 +894,7 @@ void Qcommon_Init(int argc, char **argv)
 
     Com_SetLastError(NULL);
 
-    srand(time(NULL));
+    Q_srand(time(NULL));
 
     // prepare enough of the subsystems to handle
     // cvar and command buffer management

src/server/init.c

@@ -172,8 +172,7 @@ void SV_SpawnServer(mapcmd_t *cmd)
 
     // wipe the entire per-level structure
     memset(&sv, 0, sizeof(sv));
-    sv.spawncount = (rand() | ((unsigned)rand() << 16)) ^ Sys_Milliseconds();
-    sv.spawncount &= 0x7FFFFFFF;
+    sv.spawncount = Q_rand() & 0x7fffffff;
 
     // set legacy spawncounts
     FOR_EACH_CLIENT(client) {

src/server/main.c

@@ -591,7 +591,7 @@ static void SVC_GetChallenge(void)
         }
     }
 
-    challenge = (((unsigned)rand() << 16) | rand()) & 0x7fffffff;
+    challenge = Q_rand() & 0x7fffffff;
     if (i == MAX_CHALLENGES) {
         // overwrite the oldest
         svs.challenges[oldest].challenge = challenge;

src/server/mvd/client.c

@@ -1641,8 +1641,7 @@ void MVD_Spawn(void)
 #endif
 
     // generate spawncount for Waiting Room
-    sv.spawncount = (rand() | ((unsigned)rand() << 16)) ^ Sys_Milliseconds();
-    sv.spawncount &= 0x7FFFFFFF;
+    sv.spawncount = Q_rand() & 0x7fffffff;
 
 #if USE_FPS
     // just fixed base FPS

src/server/user.c

@@ -328,7 +328,7 @@ static void stuff_junk(void)
 
     for (i = 0; i < 8; i++) {
         for (j = 0; j < 15; j++) {
-            k = rand_byte() % (sizeof(junkchars) - 1);
+            k = Q_rand() % (sizeof(junkchars) - 1);
             junk[i][j] = junkchars[k];
         }
         junk[i][15] = 0;
@@ -339,7 +339,7 @@ static void stuff_junk(void)
 
     SV_ClientCommand(sv_client, "set %s set\n", junk[0]);
     SV_ClientCommand(sv_client, "$%s %s connect\n", junk[0], junk[1]);
-    if (rand_byte() & 1) {
+    if (Q_rand() & 1) {
         SV_ClientCommand(sv_client, "$%s %s %s\n", junk[0], junk[2], junk[3]);
         SV_ClientCommand(sv_client, "$%s %s %s\n", junk[0], junk[4],
                          sv_force_reconnect->string);

src/shared/shared.c

@@ -859,6 +859,60 @@ void Q_setenv(const char *name, const char *value)
 #endif // !_WIN32
 }
 
+/*
+=====================================================================
+
+  MT19337 PRNG
+
+=====================================================================
+*/
+
+#define N 624
+#define M 397
+
+static uint32_t mt_state[N];
+static uint32_t mt_index;
+
+void Q_srand(uint32_t seed)
+{
+    mt_index = N;
+    mt_state[0] = seed;
+    for (int i = 1; i < N; i++)
+        mt_state[i] = seed = 1812433253U * (seed ^ seed >> 30) + i;
+}
+
+uint32_t Q_rand(void)
+{
+    uint32_t x, y;
+    int i;
+
+    if (mt_index >= N) {
+        mt_index = 0;
+
+#define STEP(j, k) do {                         \
+        x  = mt_state[i] &  (1U << 31);         \
+        x += mt_state[j] & ((1U << 31) - 1);    \
+        y  = x >> 1;                            \
+        y ^= 0x9908B0DF & -(x & 1);             \
+        mt_state[i] = mt_state[k] ^ y;          \
+    } while (0)
+
+        for (i = 0; i < N - M; i++)
+            STEP(i + 1, i + M);
+        for (     ; i < N - 1; i++)
+            STEP(i + 1, i - N + M);
+        STEP(0, M - 1);
+    }
+
+    y = mt_state[mt_index++];
+    y ^= y >> 11;
+    y ^= y <<  7 & 0x9D2C5680;
+    y ^= y << 15 & 0xEFC60000;
+    y ^= y >> 18;
+
+    return y;
+}
+
 /*
 =====================================================================