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Cheesemap
=========
Cheesemap is a Swiss-table HashMap implementation in C. It is designed to be fast, easy to understand, and easy to embed - the entire implementation is a single `.c` / `.h` pair with no dependencies.
The map is open-addressing with optional SIMD-accelerated control-byte matching (SSE2). It may use slightly more memory than necessary immediately after a resize and does not yet provide a shrink method. Not yet production-tested but fully functional.
## Example
```c
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "cheesemap.h"
_Noreturn void panic_impl(const char* file, cm_u32 line, const char* fmt, ...) {
fprintf(stderr, "Panic at %s:%u: ", file, line);
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
fprintf(stderr, "\n");
abort();
}
#define countof(arr) (sizeof(arr) / sizeof(*(arr)))
cm_u64 hash_string(const cm_u8* key, cm_u8* user) {
(void)user;
const char* str = *(const char**)key;
cm_u64 hash = 5381;
int c;
while ((c = *str++)) hash = ((hash << 5) + hash) + c;
return hash;
}
bool compare_string(const cm_u8* key1, const cm_u8* key2, cm_u8* user) {
(void)user;
return strcmp(*(const char**)key1, *(const char**)key2) == 0;
}
void* default_alloc(cm_usize size, cm_usize align, cm_u8* user) {
(void)user;
return aligned_alloc(align, size);
}
void default_dealloc(void* ptr, cm_u8* user) {
(void)user;
free(ptr);
}
int main(void) {
struct cheesemap map;
cm_init_(&map, const char*, int, NULL, hash_string, compare_string,
default_alloc, default_dealloc);
const char* words[] = {"hello", "world", "hello", "cheesemap", "world", "hello"};
for (size_t i = 0; i < countof(words); i++) {
int* count;
if (cm_lookup_(&map, words[i], &count)) {
(*count)++;
} else {
int initial = 1;
cm_insert_(&map, words[i], initial);
}
}
printf("Word frequencies:\n");
struct cheesemap_iter iter;
cm_iter_init(&iter, &map);
const char** word;
int* count;
while (cm_iter_next_(&iter, &map, &word, &count)) {
printf(" %s: %d\n", *word, *count);
}
const char* search = "hello";
if (cm_lookup_(&map, search, &count))
printf("\n'%s' appears %d times\n", search, *count);
const char* remove = "world";
cm_remove_(&map, remove, NULL);
printf("Removed '%s'\n", remove);
if (!cm_lookup_(&map, remove, &count))
printf("'%s' no longer in map\n", remove);
cm_drop(&map);
return 0;
}
```
## Benchmarks
Comprehensive comparison of 1,000,000 entry operations (Insert, LookupHit, LookupMiss, Erase) across multiple data types. All implementations use the same xxh_avalanche hash function. Times shown are mean values across 5 repetitions with SSE2 enabled.
**Notes:**
- absl::flat_hash_map is Google's reference Swiss table implementation
- std::unordered_map uses chained hashing (separate chaining with linked lists)
- tidwall_hashmap is a C implementation using open addressing
- All times in milliseconds (lower is better)
---
Copyright © 2026 Fabrice
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