From a10103ed9735b083200dfb78233fce325a9329dc Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 1 Nov 2025 14:21:37 -0700
Subject: Add hash library

---
 CMakeLists.txt       |  1 +
 hash/CMakeLists.txt  | 14 ++++++++++++++
 hash/include/fnv1a.h |  9 +++++++++
 hash/src/fnv1a.c     | 23 +++++++++++++++++++++++
 4 files changed, 47 insertions(+)
 create mode 100644 hash/CMakeLists.txt
 create mode 100644 hash/include/fnv1a.h
 create mode 100644 hash/src/fnv1a.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d1fb3ab..a7ce893 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,6 +8,7 @@ add_subdirectory(cassert)
 add_subdirectory(cstring)
 add_subdirectory(error)
 add_subdirectory(filesystem)
+add_subdirectory(hash)
 add_subdirectory(list)
 add_subdirectory(log)
 add_subdirectory(mem)
diff --git a/hash/CMakeLists.txt b/hash/CMakeLists.txt
new file mode 100644
index 0000000..8191f25
--- /dev/null
+++ b/hash/CMakeLists.txt
@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.5)
+
+project(hash)
+
+set(CMAKE_C_STANDARD 23)
+set(CMAKE_C_STANDARD_REQUIRED On)
+set(CMAKE_C_EXTENSIONS Off)
+
+add_library(hash
+  src/fnv1a.c)
+
+target_include_directories(hash PUBLIC include)
+
+target_compile_options(hash PRIVATE -Wall -Wextra)
diff --git a/hash/include/fnv1a.h b/hash/include/fnv1a.h
new file mode 100644
index 0000000..0d2e7cf
--- /dev/null
+++ b/hash/include/fnv1a.h
@@ -0,0 +1,9 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+uint32_t fnv1a32(const void* buffer, size_t size_bytes);
+
+uint32_t fnv1a32_begin();
+uint32_t fnv1a32_update(uint32_t hash, const void* buffer, size_t size_bytes);
diff --git a/hash/src/fnv1a.c b/hash/src/fnv1a.c
new file mode 100644
index 0000000..32cb538
--- /dev/null
+++ b/hash/src/fnv1a.c
@@ -0,0 +1,23 @@
+#include <fnv1a.h>
+
+#include <assert.h>
+
+#define FNV_PRIME        2166136261
+#define FNV_OFFSET_BASIS 16777619
+
+uint32_t fnv1a_32(const void* buffer, size_t size) {
+  assert(buffer);
+  return fnv1a32_update(fnv1a32_begin(), buffer, size);
+}
+
+uint32_t fnv1a32_begin() { return FNV_PRIME; }
+
+uint32_t fnv1a32_update(uint32_t hash, const void* buffer, size_t size) {
+  assert(buffer);
+  const uint8_t* bytes = buffer;
+  for (size_t i = 0; i < size; i++) {
+    hash = hash ^ bytes[i];
+    hash = hash * FNV_OFFSET_BASIS;
+  }
+  return hash;
+}
-- 
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