hashers now use thread local arena

Instead of writing directly to file_hashes.txt, hash_workers now are
using a local arena, writing everything once at the end

using #pragma once to ensure that a given header file is included only
once in a single compilation unit

base.h

@@ -1,11 +1,40 @@
-#ifndef BASE_H
-#define BASE_H
+#pragma once
 
 #include <assert.h>
+#include <immintrin.h>
+#include <stdatomic.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <time.h>
+
+#if defined(_WIN32) || defined(_WIN64)
+#define PLATFORM_WINDOWS 1
+#include <aclapi.h>
+#include <fcntl.h>
+#include <io.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <windows.h>
+
+#define strdup _strdup
+#else
+#include <dirent.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <pwd.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#endif
+
+#define XXH_VECTOR                                                             \
+  XXH_AVX2 // not recommanded to compile with gcc see xxhash.h line 4082
+           // Must compile with /arch:AVX2 in clang-cl or -mavx2 in clang/gcc
+#define XXH_INLINE_ALL
+#include "xxhash.c"
+#include "xxhash.h"
 
 /* ------------------------------------------------------------
    Base types
@@ -25,12 +54,14 @@ typedef int b32;
 
 typedef float f32;
 typedef double f64;
+
 /* ------------------------------------------------------------
    Size helpers
    ------------------------------------------------------------ */
 
 #define KiB(x) ((u64)(x) * 1024ULL)
 #define MiB(x) (KiB(x) * 1024ULL)
+#define GiB(x) (MiB(x) * 1024ULL)
 
 /* ------------------------------------------------------------
    Min / Max helpers
@@ -48,7 +79,7 @@ typedef double f64;
    Alignment helpers
    ------------------------------------------------------------ */
 
-#define ALIGN_UP_POW2(x, a) (((x) + ((a) - 1)) & ~((a) - 1))
+#define ALIGN_UP_POW2(x, a) ((a) ? (((x) + ((a) - 1)) & ~((a) - 1)) : (x))
 
 /* ------------------------------------------------------------
    Assert
@@ -58,4 +89,4 @@ typedef double f64;
 #define ASSERT(x) assert(x)
 #endif
 
-#endif // Base.h
+#define NDEBUG // Comment to enable asserts