Add zone allocation, internal data structures, and README

Implement mmap-based zone allocation for TINY (<=128B) and SMALL
(<=1024B) categories. malloc now creates zones on demand and
returns a pointer to the first chunk.

1 files changed, 55 insertions, 0 deletions

diff --git a/README.md b/README.md
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+# ft_malloc
+
+Custom dynamic memory allocator implementing `malloc`, `free`, and `realloc` as a shared library (`libft_malloc_$HOSTTYPE.so`).
+
+42 School project.
+
+## Build
+
+```bash
+make        # build lib/libft_malloc_$HOSTTYPE.so + symlink
+make test   # build & run tests
+make clean  # remove object files
+make fclean # full clean (library, Libft, tests)
+make re     # fclean + all
+```
+
+## Usage
+
+The library is loaded at runtime via `LD_PRELOAD`, which instructs the Linux
+dynamic linker to load the specified shared library **before** any other,
+including libc. Any symbols it exports (such as `malloc`, `free`, `realloc`)
+override the default ones. This makes it a drop-in replacement with no
+recompilation needed:
+
+```bash
+LD_PRELOAD=./lib/libft_malloc.so ./my_program
+```
+
+Every call to `malloc`, `free`, or `realloc` inside `my_program` (and any
+library it uses) will go through `ft_malloc` instead of the system allocator.
+
+## API
+
+| Function | Description |
+|---|---|
+| `void *malloc(size_t size)` | Allocate `size` bytes |
+| `void free(void *ptr)` | Release a previously allocated block |
+| `void *realloc(void *ptr, size_t size)` | Resize a block to `size` bytes |
+| `void show_alloc_mem(void)` | Print all zones and allocations to stdout |
+
+## Architecture
+
+Allocations are divided into three categories:
+
+| Category | Size range | Strategy |
+|---|---|---|
+| TINY | 1 -- 128 bytes | Pre-allocated zone (fits 100+ allocations) |
+| SMALL | 129 -- 1024 bytes | Pre-allocated zone (fits 100+ allocations) |
+| LARGE | 1025+ bytes | Individual `mmap` per allocation |
+
+TINY and SMALL zones are page-aligned regions obtained via `mmap`. New zones
+are allocated on demand when the current one is full. LARGE allocations each
+get their own `mmap` region and are released individually via `munmap`.
+
+All returned pointers are 16-byte aligned.