From 0a5204c1cc1482d555af269cdaf2980c5f76492d Mon Sep 17 00:00:00 2001
From: Richard Thier <magosit@outlook.hu>
Date: Tue, 1 Apr 2025 20:01:12 +0200
Subject: [PATCH] restrict keyword added and perf.cpp added

---
 fastrand.h | 15 ++++++++--
 perf.cpp   | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+), 2 deletions(-)
 create mode 100644 perf.cpp

diff --git a/fastrand.h b/fastrand.h
index e1d5c9d..9d9e9df 100644
--- a/fastrand.h
+++ b/fastrand.h
@@ -8,6 +8,17 @@
 #include <stdlib.h>
 #endif /* NO_CSTDLIB */
 
+#ifdef __cplusplus
+  // C++-specific logic
+  #if defined(__GNUC__) || defined(__clang__)
+    #define restrict __restrict__  // GCC/Clang
+  #elif defined(_MSC_VER)
+    #define restrict __restrict    // MSVC
+  #else
+    #error "Compiler not supported for 'restrict' keyword in C++"
+  #endif
+#endif
+
 /* Currently a single integer is enough */
 typedef uint32_t rand_state;
 
@@ -30,7 +41,7 @@ static inline uint32_t lcg(rand_state *state) {
 }
 
 /** Pick a "reasonably random" number in [0, until-1] without modulus */
-static inline uint32_t rand_until(rand_state *state, uint32_t until) {
+static inline uint32_t rand_until(rand_state *restrict state, uint32_t until) {
 	uint32_t rand = lcg(state);
 	// Multiply by "until", take the upper 32 bits of the 64-bit result
 	return (uint32_t)(((uint64_t)rand * until) >> 32);
@@ -44,7 +55,7 @@ static inline uint32_t rand_until(rand_state *state, uint32_t until) {
  * @param to The biggest possible value + 1
  * @returns A value in [from, to) interval
  */
-static inline uint32_t rand_between(rand_state *state, uint32_t from, uint32_t to) {
+static inline uint32_t rand_between(rand_state *restrict state, uint32_t from, uint32_t to) {
 	return from + rand_until(state, to - from);
 }
 
diff --git a/perf.cpp b/perf.cpp
new file mode 100644
index 0000000..2d6317f
--- /dev/null
+++ b/perf.cpp
@@ -0,0 +1,84 @@
+#include <cstdio>
+#include <cstdlib>
+#include <chrono>
+#include "fastrand.h"
+
+#define N 9999999
+#define M 99999999
+#define FROM 100
+#define TO 576
+
+int main() {
+	// Init
+	srand((unsigned int)time(NULL));
+	rand_state rs = init_rand();
+	uint32_t sum = 0; // to avoid compiler optimizing out stuff
+
+	printf("Full range generation perf - %d number of cases:\n", N);
+
+	auto t0 = std::chrono::high_resolution_clock::now();
+
+	// rand
+	for (int i = 0; i < N; ++i) {
+		sum += rand();
+	}
+
+	auto t1 = std::chrono::high_resolution_clock::now();
+
+	// arc4
+	for (int i = 0; i < N; ++i) {
+		sum += arc4random();
+	}
+
+	auto t2 = std::chrono::high_resolution_clock::now();
+
+	// lcg
+	for (int i = 0; i < N; ++i) {
+		sum += lcg(&rs);
+	}
+
+	auto t3 = std::chrono::high_resolution_clock::now();
+
+	// results 1
+
+	auto rand_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t1 - t0);
+	auto arc4_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1);
+	auto lcg_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t3 - t2);
+
+	printf("Time (rand): %.3f ms.\n", rand_elapsed.count() * 1e-6);
+	printf("Time (arc4): %.3f ms.\n", arc4_elapsed.count() * 1e-6);
+	printf("Time (lcg): %.3f ms.\n", lcg_elapsed.count() * 1e-6);
+
+	printf("Modulo VS nomod perf for rand_between (both LCG) - %d number of cases:\n", M);
+
+	auto t4 = std::chrono::high_resolution_clock::now();
+
+	// lcg + modulo
+	for (int i = 0; i < N; ++i) {
+		sum += FROM + (lcg(&rs) % (TO - FROM));
+	}
+
+	auto t5 = std::chrono::high_resolution_clock::now();
+
+	// rand_between (also LCG, but no modulus)
+	for (int i = 0; i < N; ++i) {
+		sum += rand_between(&rs, FROM, TO);
+	}
+
+	auto t6 = std::chrono::high_resolution_clock::now();
+
+	// results 2
+
+	auto mod_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t5 - t4);
+	auto between_elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(t6 - t5);
+
+	uint32_t choice = rand_between(&rs, FROM, TO);
+	printf("lcg + modulo [%u, %u): %.3f ms.\n", FROM, TO, mod_elapsed.count() * 1e-6);
+	printf("rand_between [%u, %u): %.3f ms.\n", FROM, TO, between_elapsed.count() * 1e-6);
+
+	// checksum - avoid optimizing out loops
+
+	printf("Checksum: 0x%x\n", sum);
+
+	return 0;
+}