Add split_mix_64 utility

.gitignore

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+.cache
+.DS_Store
+compile_commands.json
+outputs
+xorshift
+xorshift.dSYM

aliases.h

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+#ifndef ALIASES_H
+#define ALIASES_H
+
+#include <stdint.h>
+
+#define u8 uint8_t
+#define u16 uint16_t
+#define u32 uint32_t
+#define u64 uint64_t
+
+#define i8 int8_t
+#define i16 int16_t
+#define i32 int32_t
+#define i64 int64_t
+
+#define f32 float
+#define f64 double
+#define f128 long double
+
+#define uptr uintptr_t
+#define iptr intptr_t
+
+#define internal static
+#define persistent static
+
+#ifdef __cplusplus
+#define class_mem static
+#endif // __cplusplus
+
+#endif // !ALIASES_H

build

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+#!/bin/bash
+
+bear -- ./compile

compile

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+#!/bin/bash
+
+CC=clang
+CFLAGS="-g -Wall -Werror "
+
+XORSHIFT_SRC="xorshift.c ppm.c"
+XORSHIFT_OUT=xorshift
+
+echo "Cleaning outputs dir..."
+rm -rf "./outputs/*"
+
+echo -e "\nBuilding xorshift generators..."
+(set -x ; $CC $CFLAGS $XORSHIFT_SRC -o $XORSHIFT_OUT)
+
+echo -e "\nTesting xorshift generators..."
+./xorshift
+echo "Generated"

ppm.c

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+#include "ppm.h"
+#include "aliases.h"
+#include <stdio.h>
+#include <string.h>
+
+void write_p6_ppm(const char *filepath, Image *img) {
+  FILE *fp = fopen(filepath, "wb");
+  if (!fp) {
+    return;
+  }
+
+  char header[1024] = {0};
+  sprintf(header, "P6\n%llu %llu\n255\n", (unsigned long long)img->width,
+          (unsigned long long)img->height);
+
+  u64 length = strlen(header);
+  fwrite(&header, length, 1, fp);
+
+  u64 pixel_count = img->width * img->height;
+  fwrite(img->data, sizeof(Pixel), pixel_count, fp);
+
+  fclose(fp);
+}

ppm.h

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+#include "aliases.h"
+
+typedef struct {
+  u8 r;
+  u8 g;
+  u8 b;
+} Pixel;
+
+typedef struct {
+	u64 width;
+	u64 height;
+	Pixel *data;
+} Image;
+
+void write_p6_ppm(const char *filepath, Image *img);

xorshift.c

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+#include "aliases.h"
+#include "ppm.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+typedef struct {
+  u64 seed;
+} SplitMix64State;
+
+typedef struct {
+  u64 x;
+  u64 y;
+  u64 z;
+  u64 w;
+} XOR256State;
+
+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);
+void test_xoshiro_256p(Image *img);
+u64 xoshiro_256p_generate(void *s);
+u64 rol64(u64 x, u64 bits);
+XOR256State init_xor_256_state();
+void write_image_data(Image *img, RandGenFunc *gen_rand, void *s);
+u64 split_mix_64(SplitMix64State *state);
+
+int main(int argc, char *argv[]) {
+  struct timespec ts = {0};
+  clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
+
+  srand48(ts.tv_nsec);
+
+  u64 w = 1024;
+  u64 h = 1024;
+  u64 length = w * h;
+  Pixel data[length];
+
+  Image img = {
+      .width = w,
+      .height = h,
+      .data = data,
+  };
+
+  test_xorshift_256(&img);
+  test_xoshiro_256ss(&img);
+  test_xoshiro_256p(&img);
+
+  return EXIT_SUCCESS;
+}
+
+void test_xorshift_256(Image *img) {
+  XOR256State state = init_xor_256_state();
+  write_image_data(img, xorshift_256_generate, (void *)&state);
+  write_p6_ppm("./outputs/xorshift256.ppm", img);
+}
+
+u64 xorshift_256_generate(void *s) {
+  XOR256State *state = (XOR256State *)s;
+
+  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;
+}
+
+void test_xoshiro_256ss(Image *img) {
+  XOR256State state = init_xor_256_state();
+  write_image_data(img, xoshiro_256ss_generate, (void *)&state);
+  write_p6_ppm("./outputs/xoshiro256ss.ppm", img);
+}
+
+u64 xoshiro_256ss_generate(void *s) {
+  XOR256State *state = (XOR256State *)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;
+}
+
+void test_xoshiro_256p(Image *img) {
+  XOR256State state = init_xor_256_state();
+  write_image_data(img, xoshiro_256p_generate, (void *)&state);
+  write_p6_ppm("./outputs/xoshiro256p.ppm", img);
+}
+
+u64 xoshiro_256p_generate(void *s) {
+  XOR256State *state = (XOR256State *)s;
+
+  const u64 result = state->w + state->x;
+  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)); }
+
+XOR256State init_xor_256_state() {
+  SplitMix64State sm64 = {.seed = lrand48()};
+
+  return (XOR256State){
+      .x = split_mix_64(&sm64),
+      .y = split_mix_64(&sm64),
+      .z = split_mix_64(&sm64),
+      .w = split_mix_64(&sm64),
+  };
+}
+
+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,
+      };
+    }
+  }
+}
+
+u64 split_mix_64(SplitMix64State *state) {
+  state->seed += 0x9E3779B97f4A7C15;
+
+  u64 result = state->seed;
+  result = (result ^ (result >> 30)) * 0xBF58476D1CE4E5B9;
+  result = (result ^ (result >> 27)) * 0x94D049BB133111EB;
+
+  return result ^ (result >> 31);
+}