From f4afa5d7eacba243f5b551b6a74e4dedbfd9d0d3 Mon Sep 17 00:00:00 2001
From: Abdelrahman Said <said.abdelrahman@flawlessai.com>
Date: Fri, 22 Mar 2024 11:52:56 +0000
Subject: [PATCH] Add xoshiro256** generator

---
 xorshift.c | 93 +++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 75 insertions(+), 18 deletions(-)

diff --git a/xorshift.c b/xorshift.c
index cc21dc6..d597294 100644
--- a/xorshift.c
+++ b/xorshift.c
@@ -11,8 +11,21 @@ typedef struct {
   u64 w;
 } XORShift256;
 
-void test_xorshift_256(Pixel *data, u64 w, u64 h);
-u64 xorshift_256_generate(XORShift256 *state);
+typedef struct {
+  u64 x;
+  u64 y;
+  u64 z;
+  u64 w;
+} XOShiRo256SS;
+
+typedef u64(RandGenFunc)(void *s);
+
+void test_xorshift_256(Image *img);
+u64 xorshift_256_generate(void *s);
+void test_xoshiro_256ss(Image *img);
+u64 xoshiro_256ss_generate(void *s);
+u64 rol64(u64 x, u64 bits);
+void write_image_data(Image *img, RandGenFunc *gen_rand, void *s);
 
 int main(int argc, char *argv[]) {
   struct timespec ts = {0};
@@ -25,14 +38,22 @@ int main(int argc, char *argv[]) {
   u64 length = w * h;
   Pixel data[length];
 
-	test_xorshift_256(data, w, h);
+  Image img = {
+      .width = w,
+      .height = h,
+      .data = data,
+  };
 
-  write_p6_ppm("./outputs/xorshift_256.ppm", w, h, data);
+  test_xorshift_256(&img);
+  write_p6_ppm("./outputs/xorshift256.ppm", &img);
+
+  test_xoshiro_256ss(&img);
+  write_p6_ppm("./outputs/xoshiro256ss.ppm", &img);
 
   return EXIT_SUCCESS;
 }
 
-void test_xorshift_256(Pixel *data, u64 w, u64 h) {
+void test_xorshift_256(Image *img) {
   XORShift256 state = {
       .x = lrand48(),
       .y = lrand48(),
@@ -40,21 +61,12 @@ void test_xorshift_256(Pixel *data, u64 w, u64 h) {
       .w = lrand48(),
   };
 
-  for (u64 y = 0; y < h; ++y) {
-    for (u64 x = 0; x < w; ++x) {
-      u64 i = y * w + x;
-
-      u8 pixel = xorshift_256_generate(&state) % UINT8_MAX;
-      data[i] = (Pixel){
-          .r = pixel,
-          .g = pixel,
-          .b = pixel,
-      };
-    }
-  }
+  write_image_data(img, xorshift_256_generate, (void *)&state);
 }
 
-u64 xorshift_256_generate(XORShift256 *state) {
+u64 xorshift_256_generate(void *s) {
+  XORShift256 *state = (XORShift256 *)s;
+
   u64 t = state->x ^ (state->x << 11);
 
   state->x = state->y;
@@ -64,3 +76,48 @@ u64 xorshift_256_generate(XORShift256 *state) {
 
   return state->w;
 }
+
+void test_xoshiro_256ss(Image *img) {
+  XOShiRo256SS state = {
+      .x = lrand48(),
+      .y = lrand48(),
+      .z = lrand48(),
+      .w = lrand48(),
+  };
+
+  write_image_data(img, xoshiro_256ss_generate, (void *)&state);
+}
+
+u64 xoshiro_256ss_generate(void *s) {
+  XOShiRo256SS *state = (XOShiRo256SS *)s;
+
+  const u64 result = rol64(state->z * 5, 7) * 9;
+  const u64 t = state->z << 17;
+
+  state->y ^= state->w;
+  state->x ^= state->z;
+  state->z ^= state->y;
+  state->w ^= state->x;
+
+  state->y ^= t;
+  state->x = rol64(state->x, 45);
+
+  return result;
+}
+
+u64 rol64(u64 x, u64 bits) { return (x << bits) | (x >> (64 - bits)); }
+
+void write_image_data(Image *img, RandGenFunc *gen_rand, void *s) {
+  for (u64 y = 0; y < img->height; ++y) {
+    for (u64 x = 0; x < img->width; ++x) {
+      u64 i = y * img->width + x;
+
+      u8 pixel = gen_rand(s) % UINT8_MAX;
+      img->data[i] = (Pixel){
+          .r = pixel,
+          .g = pixel,
+          .b = pixel,
+      };
+    }
+  }
+}