# puremp

Pure-Rust, MIT-licensed, arbitrary-precision arithmetic — **integers,
rationals, and MPFR-class floating point** — with no foreign-code dependencies.
Usable as a Rust crate, a C library, and a command-line calculator.

> **Status: early scaffold.** The integer and rational layers are implemented
> and tested; the fast algorithms (sub-quadratic multiply/divide, subquadratic
> GCD) and the floating-point arithmetic layer are on the way. See
> [`ROADMAP.md`](ROADMAP.md) for the design and milestone plan.

## Why

A GMP + MPFR-class toolkit that is:

- **Pure, safe Rust** — no C, no inline assembly, no intrinsics. The only
  `unsafe` in the crate is the opt-in C ABI module.
- **Clean-room & MIT-licensed** — algorithms come from the open literature
  (Knuth; Brent & Zimmermann's *Modern Computer Arithmetic*; the HAC), never
  from GMP/MPFR source. Use it anywhere, including closed-source projects.
- **`no_std` + `alloc`** — runs on bare metal with an allocator; no OS
  assumptions in the core. Verified on 32-bit `thumbv7em-none-eabi` in CI.

## Quick start (Rust)

```toml
[dependencies]
puremp = "0"
```

```rust
use puremp::{Int, Rational};

let big = Int::from_i64(2).pow(100);
assert_eq!(big.to_string(), "1267650600228229401496703205376");

let sum = Rational::new(Int::from_i64(1), Int::from_i64(2))?   // 1/2
    .add(&Rational::new(Int::from_i64(1), Int::from_i64(3))?); // + 1/3
assert_eq!(sum.to_string(), "5/6");
# Ok::<(), puremp::Error>(())
```

## Quick start (CLI)

```console
$ cargo run --bin puremp
puremp> 2 ** 100
1267650600228229401496703205376
puremp> x = 1000
puremp> x * x - 1
999999
puremp> (2**64) * (2**64)
340282366920938463463374607431768211456
puremp> :quit
```

Supports `+ - * / % **`, parentheses, unary minus, decimal literals, and
`name = expr` variables (`/` and `%` are truncated integer division).

## Quick start (C)

Build the static and/or shared library and link against the header in
[`include/puremp.h`](include/puremp.h):

```console
$ cargo rustc --lib --release --features ffi --crate-type staticlib
$ cargo rustc --lib --release --features ffi --crate-type cdylib
$ cc myprog.c -I include target/release/libpuremp.a -lpthread -ldl -lm -o myprog
```

```c
#include "puremp.h"
#include <stdio.h>

int main(void) {
    PurempInt *two = puremp_int_from_i64(2);
    PurempInt *big = puremp_int_pow(two, 100);
    char *s = puremp_int_to_string(big);
    printf("2^100 = %s\n", s);
    puremp_string_free(s);
    puremp_int_free(big);
    puremp_int_free(two);
    return 0;
}
```

## Feature flags

| Feature | Default | Enables |
|---|:---:|---|
| `std` | ✔ | `std::error::Error`, the CLI, system I/O (implies `alloc`) |
| `alloc` | ✔ | Heap-backed arbitrary-precision types (required by every layer) |
| `int` | ✔ | `Nat` and `Int` |
| `rational` | ✔ | `Rational` (implies `int`) |
| `float` | ✔ | `Float` (implies `int`) |
| `ffi` | | The C ABI module (`include/puremp.h`) |
| `cli` | ✔ | The `puremp` binary |

For a bare `no_std` build: `--no-default-features` (add `--features int` for the
integer types).

## License

MIT — see [`LICENSE`](LICENSE).
