# Precompiles

Precompiles are built into the SP1 zkVM and accelerate commonly used operations such as elliptic curve arithmetic and hashing. Under the hood, precompiles are implemented as custom STARK tables dedicated to proving one or few operations. **They typically improve the performance
of executing expensive operations in SP1 by a few orders of magnitude.**

Inside the zkVM, precompiles are exposed as system calls executed through the `ecall`

RISC-V instruction.
Each precompile has a unique system call number and implements an interface for the computation.

SP1 also has been designed specifically to make it easy for external contributors to create and extend the zkVM with their own precompiles. To learn more about this, you can look at implementations of existing precompiles in the precompiles folder. More documentation on this will be coming soon.

**To use precompiles, we typically recommend you interact with them through patches, which are crates modified
to use these precompiles under the hood, without requiring you to call system calls directly.**

## Specification

If you are an advanced user you can interact with the precompiles directly using external system calls.

Here is a list of all available system calls & precompiles.

```
//! Syscalls for the SP1 zkVM.
//!
//! Documentation for these syscalls can be found in the zkVM entrypoint
//! `sp1_zkvm::syscalls` module.
pub mod bls12381;
pub mod bn254;
pub mod ed25519;
pub mod io;
pub mod secp256k1;
pub mod unconstrained;
pub mod utils;
#[cfg(feature = "verify")]
pub mod verify;
extern "C" {
/// Halts the program with the given exit code.
pub fn syscall_halt(exit_code: u8) -> !;
/// Writes the bytes in the given buffer to the given file descriptor.
pub fn syscall_write(fd: u32, write_buf: *const u8, nbytes: usize);
/// Reads the bytes from the given file descriptor into the given buffer.
pub fn syscall_read(fd: u32, read_buf: *mut u8, nbytes: usize);
/// Executes the SHA-256 extend operation on the given word array.
pub fn syscall_sha256_extend(w: *mut [u32; 64]);
/// Executes the SHA-256 compress operation on the given word array and a given state.
pub fn syscall_sha256_compress(w: *mut [u32; 64], state: *mut [u32; 8]);
/// Executes an Ed25519 curve addition on the given points.
pub fn syscall_ed_add(p: *mut [u32; 16], q: *const [u32; 16]);
/// Executes an Ed25519 curve decompression on the given point.
pub fn syscall_ed_decompress(point: &mut [u8; 64]);
/// Executes an Sepc256k1 curve addition on the given points.
pub fn syscall_secp256k1_add(p: *mut [u32; 16], q: *const [u32; 16]);
/// Executes an Secp256k1 curve doubling on the given point.
pub fn syscall_secp256k1_double(p: *mut [u32; 16]);
/// Executes an Secp256k1 curve decompression on the given point.
pub fn syscall_secp256k1_decompress(point: &mut [u8; 64], is_odd: bool);
/// Executes a Bn254 curve addition on the given points.
pub fn syscall_bn254_add(p: *mut [u32; 16], q: *const [u32; 16]);
/// Executes a Bn254 curve doubling on the given point.
pub fn syscall_bn254_double(p: *mut [u32; 16]);
/// Executes a BLS12-381 curve addition on the given points.
pub fn syscall_bls12381_add(p: *mut [u32; 24], q: *const [u32; 24]);
/// Executes a BLS12-381 curve doubling on the given point.
pub fn syscall_bls12381_double(p: *mut [u32; 24]);
/// Executes the Keccak-256 permutation on the given state.
pub fn syscall_keccak_permute(state: *mut [u64; 25]);
/// Executes an uint256 multiplication on the given inputs.
pub fn syscall_uint256_mulmod(x: *mut [u32; 8], y: *const [u32; 8]);
/// Enters unconstrained mode.
pub fn syscall_enter_unconstrained() -> bool;
/// Exits unconstrained mode.
pub fn syscall_exit_unconstrained();
/// Defers the verification of a valid SP1 zkVM proof.
pub fn syscall_verify_sp1_proof(vk_digest: &[u32; 8], pv_digest: &[u8; 32]);
/// Returns the length of the next element in the hint stream.
pub fn syscall_hint_len() -> usize;
/// Reads the next element in the hint stream into the given buffer.
pub fn syscall_hint_read(ptr: *mut u8, len: usize);
/// Allocates a buffer aligned to the given alignment.
pub fn sys_alloc_aligned(bytes: usize, align: usize) -> *mut u8;
/// Decompresses a BLS12-381 point.
pub fn syscall_bls12381_decompress(point: &mut [u8; 96], is_odd: bool);
/// Computes a big integer operation with a modulus.
pub fn sys_bigint(
result: *mut [u32; 8],
op: u32,
x: *const [u32; 8],
y: *const [u32; 8],
modulus: *const [u32; 8],
);
/// Executes a BLS12-381 field addition on the given inputs.
pub fn syscall_bls12381_fp_addmod(p: *mut u32, q: *const u32);
/// Executes a BLS12-381 field subtraction on the given inputs.
pub fn syscall_bls12381_fp_submod(p: *mut u32, q: *const u32);
/// Executes a BLS12-381 field multiplication on the given inputs.
pub fn syscall_bls12381_fp_mulmod(p: *mut u32, q: *const u32);
/// Executes a BLS12-381 Fp2 addition on the given inputs.
pub fn syscall_bls12381_fp2_addmod(p: *mut u32, q: *const u32);
/// Executes a BLS12-381 Fp2 subtraction on the given inputs.
pub fn syscall_bls12381_fp2_submod(p: *mut u32, q: *const u32);
/// Executes a BLS12-381 Fp2 multiplication on the given inputs.
pub fn syscall_bls12381_fp2_mulmod(p: *mut u32, q: *const u32);
/// Executes a BN254 field addition on the given inputs.
pub fn syscall_bn254_fp_addmod(p: *mut u32, q: *const u32);
/// Executes a BN254 field subtraction on the given inputs.
pub fn syscall_bn254_fp_submod(p: *mut u32, q: *const u32);
/// Executes a BN254 field multiplication on the given inputs.
pub fn syscall_bn254_fp_mulmod(p: *mut u32, q: *const u32);
/// Executes a BN254 Fp2 addition on the given inputs.
pub fn syscall_bn254_fp2_addmod(p: *mut u32, q: *const u32);
/// Executes a BN254 Fp2 subtraction on the given inputs.
pub fn syscall_bn254_fp2_submod(p: *mut u32, q: *const u32);
/// Executes a BN254 Fp2 multiplication on the given inputs.
pub fn syscall_bn254_fp2_mulmod(p: *mut u32, q: *const u32);
}
```