Added SDL_srand(), SDL_rand(), and SDL_rand_r() (thanks @JKaniarz!)

These are simple random functions that should not be used for serious random number generation.

Fixes https://github.com/libsdl-org/SDL/issues/4968

src/dynapi/SDL_dynapi.sym

@@ -955,6 +955,8 @@ SDL3_0.0.0 {
     SDL_powf;
     SDL_qsort;
     SDL_qsort_r;
+    SDL_rand;
+    SDL_rand_r;
     SDL_realloc;
     SDL_round;
     SDL_roundf;
@@ -966,6 +968,7 @@ SDL3_0.0.0 {
     SDL_snprintf;
     SDL_sqrt;
     SDL_sqrtf;
+    SDL_srand;
     SDL_sscanf;
     SDL_strcasecmp;
     SDL_strcasestr;

src/dynapi/SDL_dynapi_overrides.h

@@ -980,6 +980,8 @@
 #define SDL_powf SDL_powf_REAL
 #define SDL_qsort SDL_qsort_REAL
 #define SDL_qsort_r SDL_qsort_r_REAL
+#define SDL_rand SDL_rand_REAL
+#define SDL_rand_r SDL_rand_r_REAL
 #define SDL_realloc SDL_realloc_REAL
 #define SDL_round SDL_round_REAL
 #define SDL_roundf SDL_roundf_REAL
@@ -991,6 +993,7 @@
 #define SDL_snprintf    SDL_snprintf_REAL
 #define SDL_sqrt SDL_sqrt_REAL
 #define SDL_sqrtf SDL_sqrtf_REAL
+#define SDL_srand SDL_srand_REAL
 #define SDL_sscanf  SDL_sscanf_REAL
 #define SDL_strcasecmp SDL_strcasecmp_REAL
 #define SDL_strcasestr SDL_strcasestr_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -989,6 +989,8 @@ SDL_DYNAPI_PROC(double,SDL_pow,(double a, double b),(a,b),return)
 SDL_DYNAPI_PROC(float,SDL_powf,(float a, float b),(a,b),return)
 SDL_DYNAPI_PROC(void,SDL_qsort,(void *a, size_t b, size_t c, SDL_CompareCallback d),(a,b,c,d),)
 SDL_DYNAPI_PROC(void,SDL_qsort_r,(void *a, size_t b, size_t c, SDL_CompareCallback_r d, void *e),(a,b,c,d,e),)
+SDL_DYNAPI_PROC(Uint32,SDL_rand,(void),(),return)
+SDL_DYNAPI_PROC(Uint32,SDL_rand_r,(Uint64 *a),(a),return)
 SDL_DYNAPI_PROC(void*,SDL_realloc,(void *a, size_t b),(a,b),return)
 SDL_DYNAPI_PROC(double,SDL_round,(double a),(a),return)
 SDL_DYNAPI_PROC(float,SDL_roundf,(float a),(a),return)
@@ -999,6 +1001,7 @@ SDL_DYNAPI_PROC(double,SDL_sin,(double a),(a),return)
 SDL_DYNAPI_PROC(float,SDL_sinf,(float a),(a),return)
 SDL_DYNAPI_PROC(double,SDL_sqrt,(double a),(a),return)
 SDL_DYNAPI_PROC(float,SDL_sqrtf,(float a),(a),return)
+SDL_DYNAPI_PROC(void,SDL_srand,(Uint64 a),(a),)
 SDL_DYNAPI_PROC(int,SDL_strcasecmp,(const char *a, const char *b),(a,b),return)
 SDL_DYNAPI_PROC(char*,SDL_strcasestr,(const char *a, const char *b),(a,b),return)
 SDL_DYNAPI_PROC(char*,SDL_strchr,(const char *a, int b),(a,b),return)

src/stdlib/SDL_random.c

@@ -0,0 +1,80 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+/* This file contains portable random functions for SDL */
+
+static Uint64 SDL_rand_state;
+
+void SDL_srand(Uint64 seed)
+{
+    SDL_rand_state = seed;
+}
+
+Uint32 SDL_rand(void)
+{
+	return SDL_rand_r(&SDL_rand_state);
+}
+
+/*
+ * Return a number between [0, n)
+ * Fast but slightly biased. Don't run your casino with this.
+ */
+Sint32 SDL_rand_n(Sint32 n)
+{
+	// On 32-bit arch, the compiler will optimize to a single 32-bit multiply
+	Uint64 val = (Uint64)SDL_rand() * n;
+	return (Sint32)(val >> 32);
+}
+
+/*
+ * Random float in range [0,1)
+ */
+float SDL_rand_float(void)
+{
+	return (SDL_rand() >> (32-24)) * 0x1p-24f;
+}
+
+/* A fast psuedo-random number generator.
+ * Not suitable for cryptography or gambling
+ */
+Uint32 SDL_rand_r(Uint64 *state)
+{
+    if (!state) {
+        return 0;
+    }
+
+    if (!*state) {
+        *state = SDL_GetPerformanceCounter();
+    }
+
+	// Multiplier from Table 6 of
+	// Steele GL, Vigna S. Computationally easy, spectrally good multipliers
+	// for congruential pseudorandom number generators.
+	// Softw Pract Exper. 2022;52(2):443-458. doi: 10.1002/spe.3030
+
+	// 32-bit 'a' improves performance on 32-bit architectures
+	// 'c' can be any odd number, but < 256 generates smaller code on some arch
+	*state = *state * 0xf9b25d65ul + 0xFD;
+
+	// Only return top 32 bits because they have a longer period
+	return (Uint32)(*state >> 32);
+}