From f8217d240d598f39f70047f7a623dd46312542c6 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 4 Dec 2021 16:01:12 -0800
Subject: Initial commit.

---
 mempool/src/mempool.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 mempool/src/mempool.c

(limited to 'mempool/src')

diff --git a/mempool/src/mempool.c b/mempool/src/mempool.c
new file mode 100644
index 0000000..b7e8705
--- /dev/null
+++ b/mempool/src/mempool.c
@@ -0,0 +1,85 @@
+#include "mempool.h"
+
+#include <string.h>
+
+static inline size_t min(size_t a, size_t b) { return a < b ? a : b; }
+
+void mempool_make_(mempool* pool, BlockInfo* block_info, void* blocks,
+                   size_t num_blocks, size_t block_size_bytes) {
+  assert(pool);
+  assert(block_info);
+  assert(blocks);
+  assert(num_blocks >= 1);
+  pool->block_size_bytes = block_size_bytes;
+  pool->num_blocks = num_blocks;
+  pool->next_free_block = 0;
+  pool->full = false;
+  pool->block_info = block_info;
+  pool->blocks = blocks;
+  memset(blocks, 0, num_blocks * block_size_bytes);
+}
+
+void* mempool_alloc_(mempool* pool) {
+  assert(pool);
+
+  if (pool->full) {
+    return 0;
+  }
+
+  // Allocate the block.
+  void* block = &pool->blocks[pool->next_free_block * pool->block_size_bytes];
+  pool->block_info[pool->next_free_block].used = true;
+
+  // Search for the next free block. If it does not exist, flag the pool full.
+  pool->full = true;
+  for (size_t i = 1; i < pool->num_blocks && i != 0; i++) {
+    pool->next_free_block = (pool->next_free_block + 1) % pool->num_blocks;
+    if (!pool->block_info[pool->next_free_block].used) {
+      pool->full = false;
+      break;
+    }
+  }
+
+  return block;
+}
+
+void mempool_free_(mempool* pool, void** block_ptr) {
+  assert(pool);
+  assert(block_ptr);
+
+  memset(*block_ptr, 0, pool->block_size_bytes);
+
+  const size_t block_index =
+      ((uint8_t*)*block_ptr - pool->blocks) / pool->block_size_bytes;
+  assert(block_index < pool->num_blocks);
+
+  // Disallow double-frees.
+  assert(pool->block_info[block_index].used);
+
+  pool->block_info[block_index].used = false;
+  if (pool->full) {
+    pool->next_free_block = block_index;
+    pool->full = false;
+  } else {
+    // Prefer to allocate blocks towards the start of the pool. This way, blocks
+    // should cluster around this area and the pool should offer better memory
+    // locality for used blocks.
+    pool->next_free_block = min(pool->next_free_block, block_index);
+  }
+
+  *block_ptr = 0;
+}
+
+void* mempool_get_block_(const mempool* pool, size_t block_index) {
+  assert(pool);
+  assert(block_index < pool->num_blocks);
+  assert(pool->block_info[block_index].used);
+  return pool->blocks + block_index * pool->block_size_bytes;
+}
+
+size_t mempool_get_block_index_(const mempool* pool, const void* block) {
+  assert(pool);
+  const size_t block_byte_index = (const uint8_t*)block - pool->blocks;
+  assert(block_byte_index % pool->block_size_bytes == 0);
+  return block_byte_index / pool->block_size_bytes;
+}
-- 
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