From b2bd93ce391765f296fca4ab4705fc62e0c62060 Mon Sep 17 00:00:00 2001
From: Abdelrahman Said <said.abdelrahman89@gmail.com>
Date: Fri, 22 Mar 2024 00:26:01 +0000
Subject: [PATCH] Implement basic xorshift PRNG

---
 xorshift.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 xorshift.c

diff --git a/xorshift.c b/xorshift.c
new file mode 100644
index 0000000..2c88676
--- /dev/null
+++ b/xorshift.c
@@ -0,0 +1,63 @@
+#include "aliases.h"
+#include "ppm.h"
+#include <bits/time.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+typedef struct {
+  u64 x;
+  u64 y;
+  u64 z;
+  u64 w;
+} XORShiftBasic;
+
+u64 xor_shift_basic_generate(XORShiftBasic *state);
+
+int main(int argc, char *argv[]) {
+  struct timespec ts = {0};
+  clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
+
+  srand48(ts.tv_nsec);
+
+  XORShiftBasic state = {
+      .x = lrand48(),
+      .y = lrand48(),
+      .z = lrand48(),
+      .w = lrand48(),
+  };
+
+  u64 w = 1024;
+  u64 h = 1024;
+  u64 length = w * h;
+
+  Pixel data[length];
+  for (u64 y = 0; y < h; ++y) {
+    for (u64 x = 0; x < w; ++x) {
+      u64 i = y * w + x;
+
+      u8 pixel = xor_shift_basic_generate(&state) % UINT8_MAX;
+      data[i] = (Pixel){
+          .r = pixel,
+          .g = pixel,
+          .b = pixel,
+      };
+    }
+  }
+
+  write_p6_ppm("./outputs/xorshift.ppm", w, h, data);
+
+  return EXIT_SUCCESS;
+}
+
+u64 xor_shift_basic_generate(XORShiftBasic *state) {
+  u64 t = state->x ^ (state->x << 11);
+
+  state->x = state->y;
+  state->y = state->z;
+  state->z = state->w;
+  state->w = (state->w ^ (state->w >> 19)) ^ (t ^ (t >> 8));
+
+  return state->w;
+}