cross platform random numbers for samples

erincatto · Aug 31, 2024 · 1b57543 · 1b57543
1 parent e6cbbfc
commit 1b57543
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Showing 3 changed files with 30 additions and 11 deletions.
diff --git a/samples/sample.cpp b/samples/sample.cpp
@@ -101,6 +101,8 @@ Sample::Sample( Settings& settings )
 	m_maxProfile = {};
 	m_totalProfile = {};
 
+	g_seed = RAND_SEED;
+
 	TestMathCpp();
 }
 
@@ -488,10 +490,12 @@ int RegisterSample( const char* category, const char* name, SampleCreateFcn* fcn
 	return -1;
 }
 
+uint32_t g_seed = RAND_SEED;
+
 b2Polygon RandomPolygon( float extent )
 {
 	b2Vec2 points[b2_maxPolygonVertices];
-	int count = 3 + rand() % 6;
+	int count = 3 + RandomInt() % 6;
 	for ( int i = 0; i < count; ++i )
 	{
 		points[i] = RandomVec2( -extent, extent );

diff --git a/samples/sample.h b/samples/sample.h
@@ -10,8 +10,6 @@
 // todo this include is slow
 #include "TaskScheduler.h"
 
-#include <stdlib.h>
-
 #define ARRAY_COUNT( A ) (int)( sizeof( A ) / sizeof( A[0] ) )
 
 struct Settings;
@@ -113,32 +111,49 @@ extern SampleEntry g_sampleEntries[MAX_SAMPLES];
 extern int g_sampleCount;
 
 #define RAND_LIMIT 32767
+#define RAND_SEED 12345
+
+extern uint32_t g_seed;
+
+// Generate the next random number
+inline int RandomInt()
+{
+	// XorShift32 algorithm
+	uint32_t x = g_seed;
+	x ^= x << 13;
+	x ^= x >> 17;
+	x ^= x << 5;
+	g_seed = x;
+
+	// Map the 32-bit value to the range 0 to RAND_LIMIT
+	return (int)( x % ( RAND_LIMIT + 1 ) );
+}
 
-/// Random integer in range [lo, hi)
+// Random integer in range [lo, hi]
 inline float RandomInt( int lo, int hi )
 {
-	return lo + rand() % ( hi - lo );
+	return lo + RandomInt() % ( hi - lo + 1 );
 }
 
-/// Random number in range [-1,1]
+// Random number in range [-1,1]
 inline float RandomFloat()
 {
-	float r = (float)( rand() & ( RAND_LIMIT ) );
+	float r = (float)( RandomInt() & ( RAND_LIMIT ) );
 	r /= RAND_LIMIT;
 	r = 2.0f * r - 1.0f;
 	return r;
 }
 
-/// Random floating point number in range [lo, hi]
+// Random floating point number in range [lo, hi]
 inline float RandomFloat( float lo, float hi )
 {
-	float r = (float)( rand() & ( RAND_LIMIT ) );
+	float r = (float)( RandomInt() & ( RAND_LIMIT ) );
 	r /= RAND_LIMIT;
 	r = ( hi - lo ) * r + lo;
 	return r;
 }
 
-/// Random vector with coordinates in range [lo, hi]
+// Random vector with coordinates in range [lo, hi]
 inline b2Vec2 RandomVec2( float lo, float hi )
 {
 	b2Vec2 v;

diff --git a/samples/sample_benchmark.cpp b/samples/sample_benchmark.cpp
@@ -74,7 +74,7 @@ class BenchmarkBarrel : public Sample
 
 	void CreateScene()
 	{
-		srand( 42 );
+		g_seed = 42;
 
 		for ( int i = 0; i < e_maxRows * e_maxColumns; ++i )
 		{