openethereum/ethash/src/compute.rs

// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

//! Ethash implementation
//! See https://github.com/ethereum/wiki/wiki/Ethash

// TODO: fix endianess for big endian

use primal::is_prime;
use std::cell::Cell;
use std::mem;
use std::ptr;
use sha3;
use std::slice;
use std::path::{Path, PathBuf};
use std::io::{self, Read, Write};
use std::fs::{self, File};

use parking_lot::Mutex;

pub const ETHASH_EPOCH_LENGTH: u64 = 30000;
pub const ETHASH_CACHE_ROUNDS: usize = 3;
pub const ETHASH_MIX_BYTES: usize = 128;
pub const ETHASH_ACCESSES: usize = 64;
pub const ETHASH_DATASET_PARENTS: u32 = 256;

const DATASET_BYTES_INIT: u64 = 1 << 30;
const DATASET_BYTES_GROWTH: u64 = 1 << 23;
const CACHE_BYTES_INIT: u64 = 1 << 24;
const CACHE_BYTES_GROWTH: u64 = 1 << 17;
const NODE_WORDS: usize = 64 / 4;
const NODE_BYTES: usize = 64;
const MIX_WORDS: usize = ETHASH_MIX_BYTES / 4;
const MIX_NODES: usize = MIX_WORDS / NODE_WORDS;
const FNV_PRIME: u32 = 0x01000193;

/// Computation result
pub struct ProofOfWork {
	/// Difficulty boundary
	pub value: H256,
	/// Mix
	pub mix_hash: H256,
}

struct Node {
	bytes: [u8; NODE_BYTES],
}

impl Default for Node {
	fn default() -> Self {
		Node { bytes: [0u8; NODE_BYTES] }
	}
}

impl Clone for Node {
	fn clone(&self) -> Self {
		Node { bytes: *&self.bytes }
	}
}

impl Node {
	#[inline]
	fn as_words(&self) -> &[u32; NODE_WORDS] {
		unsafe { mem::transmute(&self.bytes) }
	}

	#[inline]
	fn as_words_mut(&mut self) -> &mut [u32; NODE_WORDS] {
		unsafe { mem::transmute(&mut self.bytes) }
	}
}

pub type H256 = [u8; 32];

pub struct Light {
	cache_dir: PathBuf,
	block_number: u64,
	cache: Vec<Node>,
	seed_compute: Mutex<SeedHashCompute>,
}

/// Light cache structure
impl Light {
	/// Create a new light cache for a given block number
	pub fn new<T: AsRef<Path>>(cache_dir: T, block_number: u64) -> Light {
		light_new(cache_dir, block_number)
	}

	/// Calculate the light boundary data
	/// `header_hash` - The header hash to pack into the mix
	/// `nonce` - The nonce to pack into the mix
	pub fn compute(&self, header_hash: &H256, nonce: u64) -> ProofOfWork {
		light_compute(self, header_hash, nonce)
	}

	pub fn file_path<T: AsRef<Path>>(cache_dir: T, seed_hash: H256) -> PathBuf {
		let mut cache_dir = cache_dir.as_ref().to_path_buf();
		cache_dir.push(to_hex(&seed_hash));
		cache_dir
	}

	pub fn from_file<T: AsRef<Path>>(cache_dir: T, block_number: u64) -> io::Result<Light> {
		let seed_compute = SeedHashCompute::new();
		let path = Light::file_path(&cache_dir, seed_compute.get_seedhash(block_number));
		let mut file = File::open(path)?;

		let cache_size = get_cache_size(block_number);
		if file.metadata()?.len() != cache_size as u64 {
			return Err(io::Error::new(io::ErrorKind::Other, "Cache file size mismatch"));
		}
		let num_nodes = cache_size / NODE_BYTES;
		let mut nodes: Vec<Node> = Vec::with_capacity(num_nodes);

		unsafe { nodes.set_len(num_nodes) };

		let buf = unsafe { slice::from_raw_parts_mut(nodes.as_mut_ptr() as *mut u8, cache_size) };
		file.read_exact(buf)?;
		Ok(Light {
			block_number,
			cache_dir: cache_dir.as_ref().to_path_buf(),
			cache: nodes,
			seed_compute: Mutex::new(seed_compute),
		})
	}

	pub fn to_file(&self) -> io::Result<PathBuf> {
		let seed_compute = self.seed_compute.lock();
		let path = Light::file_path(&self.cache_dir, seed_compute.get_seedhash(self.block_number));

		if self.block_number >= ETHASH_EPOCH_LENGTH * 2 {
			let deprecated = Light::file_path(
				&self.cache_dir,
				seed_compute.get_seedhash(self.block_number - ETHASH_EPOCH_LENGTH * 2)
			);

			if deprecated.exists() {
				debug!(target: "ethash", "removing: {:?}", &deprecated);
				fs::remove_file(deprecated)?;
			}
		}

		fs::create_dir_all(path.parent().unwrap())?;
		let mut file = File::create(&path)?;

		let cache_size = self.cache.len() * NODE_BYTES;
		let buf = unsafe { slice::from_raw_parts(self.cache.as_ptr() as *const u8, cache_size) };
		file.write(buf)?;
		Ok(path)
	}
}

pub struct SeedHashCompute {
	prev_epoch: Cell<u64>,
	prev_seedhash: Cell<H256>,
}

impl SeedHashCompute {
	#[inline]
	pub fn new() -> SeedHashCompute {
		SeedHashCompute {
			prev_epoch: Cell::new(0),
			prev_seedhash: Cell::new([0u8; 32]),
		}
	}

	#[inline]
	fn reset_cache(&self) {
		self.prev_epoch.set(0);
		self.prev_seedhash.set([0u8; 32]);
	}

	#[inline]
	pub fn get_seedhash(&self, block_number: u64) -> H256 {
		let epoch = block_number / ETHASH_EPOCH_LENGTH;
		if epoch < self.prev_epoch.get() {
			// can't build on previous hash if requesting an older block
			self.reset_cache();
		}
		if epoch > self.prev_epoch.get() {
			let seed_hash = SeedHashCompute::resume_compute_seedhash(self.prev_seedhash.get(), self.prev_epoch.get(), epoch);
			self.prev_seedhash.set(seed_hash);
			self.prev_epoch.set(epoch);
		}
		self.prev_seedhash.get()
	}

	#[inline]
	pub fn resume_compute_seedhash(mut hash: H256, start_epoch: u64, end_epoch: u64) -> H256 {
		for _ in start_epoch..end_epoch {
			unsafe { sha3::sha3_256(hash[..].as_mut_ptr(), 32, hash[..].as_ptr(), 32) };
		}
		hash
	}
}

pub fn slow_get_seedhash(block_number: u64) -> H256 {
	SeedHashCompute::resume_compute_seedhash([0u8; 32], 0, block_number / ETHASH_EPOCH_LENGTH)
}

fn fnv_hash(x: u32, y: u32) -> u32 {
	return x.wrapping_mul(FNV_PRIME) ^ y;
}

fn sha3_512(input: &[u8], output: &mut [u8]) {
	unsafe { sha3::sha3_512(output.as_mut_ptr(), output.len(), input.as_ptr(), input.len()) };
}

fn sha3_512_inplace(input: &mut [u8]) {
	// This is safe since `sha3_*` uses an internal buffer and copies the result to the output. This
	// means that we can reuse the input buffer for both input and output.
	unsafe { sha3::sha3_512(input.as_mut_ptr(), input.len(), input.as_ptr(), input.len()) };
}

fn get_cache_size(block_number: u64) -> usize {
	let mut sz: u64 = CACHE_BYTES_INIT + CACHE_BYTES_GROWTH * (block_number / ETHASH_EPOCH_LENGTH);
	sz = sz - NODE_BYTES as u64;
	while !is_prime(sz / NODE_BYTES as u64) {
		sz = sz - 2 * NODE_BYTES as u64;
	}
	sz as usize
}

fn get_data_size(block_number: u64) -> usize {
	let mut sz: u64 = DATASET_BYTES_INIT + DATASET_BYTES_GROWTH * (block_number / ETHASH_EPOCH_LENGTH);
	sz = sz - ETHASH_MIX_BYTES as u64;
	while !is_prime(sz / ETHASH_MIX_BYTES as u64) {
		sz = sz - 2 * ETHASH_MIX_BYTES as u64;
	}
	sz as usize
}

/// Difficulty quick check for POW preverification
///
/// `header_hash`      The hash of the header
/// `nonce`            The block's nonce
/// `mix_hash`         The mix digest hash
/// Boundary recovered from mix hash
pub fn quick_get_difficulty(header_hash: &H256, nonce: u64, mix_hash: &H256) -> H256 {
	unsafe {
		// This is safe - the `sha3_512` call below reads the first 40 bytes (which we explicitly set
		// with two `copy_nonoverlapping` calls) but writes the first 64, and then we explicitly write
		// the next 32 bytes before we read the whole thing with `sha3_256`.
		//
		// This cannot be elided by the compiler as it doesn't know the implementation of
		// `sha3_512`.
		let mut buf: [u8; 64 + 32] = mem::uninitialized();

		ptr::copy_nonoverlapping(header_hash.as_ptr(), buf.as_mut_ptr(), 32);
		ptr::copy_nonoverlapping(mem::transmute(&nonce), buf[32..].as_mut_ptr(), 8);

		sha3::sha3_512(buf.as_mut_ptr(), 64, buf.as_ptr(), 40);
		ptr::copy_nonoverlapping(mix_hash.as_ptr(), buf[64..].as_mut_ptr(), 32);

		// This is initialized in `sha3_256`
		let mut hash: [u8; 32] = mem::uninitialized();
		sha3::sha3_256(hash.as_mut_ptr(), hash.len(), buf.as_ptr(), buf.len());

		hash
	}
}

/// Calculate the light client data
/// `light` - The light client handler
/// `header_hash` - The header hash to pack into the mix
/// `nonce` - The nonce to pack into the mix
pub fn light_compute(light: &Light, header_hash: &H256, nonce: u64) -> ProofOfWork {
	let full_size = get_data_size(light.block_number);
	hash_compute(light, full_size, header_hash, nonce)
}

fn hash_compute(light: &Light, full_size: usize, header_hash: &H256, nonce: u64) -> ProofOfWork {
	macro_rules! make_const_array {
		($n:expr, $value:expr) => {{
			// We use explicit lifetimes to ensure that val's borrow is invalidated until the
			// transmuted val dies.
			unsafe fn make_const_array<'a, T, U>(val: &'a mut [T]) -> &'a mut [U; $n] {
				use ::std::mem;

				debug_assert_eq!(val.len() * mem::size_of::<T>(), $n * mem::size_of::<U>());
				mem::transmute(val.as_mut_ptr())
			}

			make_const_array($value)
		}}
	}

	#[repr(C)]
	struct MixBuf {
		half_mix: Node,
		compress_bytes: [u8; MIX_WORDS],
	};

	if full_size % MIX_WORDS != 0 {
		panic!("Unaligned full size");
	}

	// You may be asking yourself: what in the name of Crypto Jesus is going on here? So: we need
	// `half_mix` and `compress_bytes` in a single array later down in the code (we hash them
	// together to create `value`) so that we can hash the full array. However, we do a bunch of
	// reading and writing to these variables first. We originally allocated two arrays and then
	// stuck them together with `ptr::copy_nonoverlapping` at the end, but this method is
	// _significantly_ faster - by my benchmarks, a consistent 3-5%. This is the most ridiculous
	// optimization I have ever done and I am so sorry. I can only chalk it up to cache locality
	// improvements, since I can't imagine that 3-5% of our runtime is taken up by catting two
	// arrays together.
	let mut buf: MixBuf = MixBuf {
		half_mix: unsafe {
			// Pack `header_hash` and `nonce` together
			// We explicitly write the first 40 bytes, leaving the last 24 as uninitialized. Then
			// `sha3_512` reads the first 40 bytes (4th parameter) and overwrites the entire array,
			// leaving it fully initialized.
			let mut out: [u8; NODE_BYTES] = mem::uninitialized();

			ptr::copy_nonoverlapping(
				header_hash.as_ptr(),
				out.as_mut_ptr(),
				header_hash.len(),
			);
			ptr::copy_nonoverlapping(
				mem::transmute(&nonce),
				out[header_hash.len()..].as_mut_ptr(),
				mem::size_of::<u64>(),
			);

			// compute sha3-512 hash and replicate across mix
			sha3::sha3_512(
				out.as_mut_ptr(),
				NODE_BYTES,
				out.as_ptr(),
				header_hash.len() + mem::size_of::<u64>()
			);

			Node { bytes: out }
		},
		// This is fully initialized before being read, see `let mut compress = ...` below
		compress_bytes: unsafe { mem::uninitialized() },
	};

	let mut mix: [_; MIX_NODES] = [buf.half_mix.clone(), buf.half_mix.clone()];

	let page_size = 4 * MIX_WORDS;
	let num_full_pages = (full_size / page_size) as u32;
	// deref once for better performance
	let cache: &[Node] = &light.cache;
	let first_val = buf.half_mix.as_words()[0];

	debug_assert_eq!(MIX_NODES, 2);
	debug_assert_eq!(NODE_WORDS, 16);

	for i in 0..ETHASH_ACCESSES as u32 {
		let index = {
			// This is trivially safe, but does not work on big-endian. The safety of this is
			// asserted in debug builds (see the definition of `make_const_array!`).
			let mix_words: &mut [u32; MIX_WORDS] = unsafe {
				make_const_array!(MIX_WORDS, &mut mix)
			};

			fnv_hash(
				first_val ^ i,
				mix_words[i as usize % MIX_WORDS]
			) % num_full_pages
		};

		unroll! {
			// MIX_NODES
			for n in 0..2 {
				let tmp_node = calculate_dag_item(
					index * MIX_NODES as u32 + n as u32,
					cache,
				);

				unroll! {
					// NODE_WORDS
					for w in 0..16 {
						mix[n].as_words_mut()[w] =
							fnv_hash(
								mix[n].as_words()[w],
								tmp_node.as_words()[w],
							);
					}
				}
			}
		}
	}

	let mix_words: [u32; MIX_WORDS] = unsafe { mem::transmute(mix) };

	{
		// This is an uninitialized buffer to begin with, but we iterate precisely `compress.len()`
		// times and set each index, leaving the array fully initialized. THIS ONLY WORKS ON LITTLE-
		// ENDIAN MACHINES. See a future PR to make this and the rest of the code work correctly on
		// big-endian arches like mips.
		let mut compress: &mut [u32; MIX_WORDS / 4] = unsafe {
			make_const_array!(MIX_WORDS / 4, &mut buf.compress_bytes)
		};

		// Compress mix
		debug_assert_eq!(MIX_WORDS / 4, 8);
		unroll! {
			for i in 0..8 {
				let w = i * 4;

				let mut reduction = mix_words[w + 0];
				reduction = reduction.wrapping_mul(FNV_PRIME) ^ mix_words[w + 1];
				reduction = reduction.wrapping_mul(FNV_PRIME) ^ mix_words[w + 2];
				reduction = reduction.wrapping_mul(FNV_PRIME) ^ mix_words[w + 3];
				compress[i] = reduction;
			}
		}
	}

	let mix_hash = buf.compress_bytes;

	let value: H256 = unsafe {
		// We can interpret the buffer as an array of `u8`s, since it's `repr(C)`.
		let read_ptr: *const u8 = mem::transmute(&buf);
		// We overwrite the second half since `sha3_256` has an internal buffer and so allows
		// overlapping arrays as input.
		let write_ptr: *mut u8 = mem::transmute(&mut buf.compress_bytes);
		sha3::sha3_256(
			write_ptr,
			buf.compress_bytes.len(),
			read_ptr,
			buf.half_mix.bytes.len() + buf.compress_bytes.len(),
		);
		buf.compress_bytes
	};

	ProofOfWork {
		mix_hash: mix_hash,
		value: value,
	}
}

fn calculate_dag_item(node_index: u32, cache: &[Node]) -> Node {
	let num_parent_nodes = cache.len();
	let mut ret = cache[node_index as usize % num_parent_nodes].clone();
	ret.as_words_mut()[0] ^= node_index;

	sha3_512_inplace(&mut ret.bytes);

	debug_assert_eq!(NODE_WORDS, 16);
	for i in 0..ETHASH_DATASET_PARENTS as u32 {
		let parent_index = fnv_hash(
			node_index ^ i,
			ret.as_words()[i as usize % NODE_WORDS],
		) % num_parent_nodes as u32;
		let parent = &cache[parent_index as usize];

		unroll! {
			for w in 0..16 {
				ret.as_words_mut()[w] = fnv_hash(ret.as_words()[w], parent.as_words()[w]);
			}
		}
	}

	sha3_512_inplace(&mut ret.bytes);

	ret
}

fn light_new<T: AsRef<Path>>(cache_dir: T, block_number: u64) -> Light {
	let seed_compute = SeedHashCompute::new();
	let seedhash = seed_compute.get_seedhash(block_number);
	let cache_size = get_cache_size(block_number);

	assert!(cache_size % NODE_BYTES == 0, "Unaligned cache size");
	let num_nodes = cache_size / NODE_BYTES;

	let mut nodes: Vec<Node> = Vec::with_capacity(num_nodes);
	unsafe {
		// Use uninit instead of unnecessarily writing `size_of::<Node>() * num_nodes` 0s
		nodes.set_len(num_nodes);

		sha3_512(&seedhash[0..32], &mut nodes.get_unchecked_mut(0).bytes);
		for i in 1..num_nodes {
			sha3::sha3_512(nodes.get_unchecked_mut(i).bytes.as_mut_ptr(), NODE_BYTES, nodes.get_unchecked(i - 1).bytes.as_ptr(), NODE_BYTES);
		}

		debug_assert_eq!(NODE_WORDS, 16);

		// This _should_ get unrolled by the compiler, since it's not using the loop variable.
		for _ in 0..ETHASH_CACHE_ROUNDS {
			for i in 0..num_nodes {
				let idx = *nodes.get_unchecked_mut(i).as_words().get_unchecked(0) as usize % num_nodes;
				let mut data = nodes.get_unchecked((num_nodes - 1 + i) % num_nodes).clone();

				unroll! {
					for w in 0..16 {
						*data.as_words_mut().get_unchecked_mut(w) ^= *nodes.get_unchecked(idx).as_words().get_unchecked(w);
					}
				}

				sha3_512(&data.bytes, &mut nodes.get_unchecked_mut(i).bytes);
			}
		}
	}

	Light {
		block_number,
		cache_dir: cache_dir.as_ref().to_path_buf(),
		cache: nodes,
		seed_compute: Mutex::new(seed_compute),
	}
}

static CHARS: &'static [u8] = b"0123456789abcdef";
fn to_hex(bytes: &[u8]) -> String {
	let mut v = Vec::with_capacity(bytes.len() * 2);
	for &byte in bytes.iter() {
		v.push(CHARS[(byte >> 4) as usize]);
		v.push(CHARS[(byte & 0xf) as usize]);
	}

	unsafe { String::from_utf8_unchecked(v) }
}

#[test]
fn test_get_cache_size() {
	// https://github.com/ethereum/wiki/wiki/Ethash/ef6b93f9596746a088ea95d01ca2778be43ae68f#data-sizes
	assert_eq!(16776896usize, get_cache_size(0));
	assert_eq!(16776896usize, get_cache_size(1));
	assert_eq!(16776896usize, get_cache_size(ETHASH_EPOCH_LENGTH - 1));
	assert_eq!(16907456usize, get_cache_size(ETHASH_EPOCH_LENGTH));
	assert_eq!(16907456usize, get_cache_size(ETHASH_EPOCH_LENGTH + 1));
	assert_eq!(284950208usize, get_cache_size(2046 * ETHASH_EPOCH_LENGTH));
	assert_eq!(285081536usize, get_cache_size(2047 * ETHASH_EPOCH_LENGTH));
	assert_eq!(285081536usize, get_cache_size(2048 * ETHASH_EPOCH_LENGTH - 1));
}

#[test]
fn test_get_data_size() {
	// https://github.com/ethereum/wiki/wiki/Ethash/ef6b93f9596746a088ea95d01ca2778be43ae68f#data-sizes
	assert_eq!(1073739904usize, get_data_size(0));
	assert_eq!(1073739904usize, get_data_size(1));
	assert_eq!(1073739904usize, get_data_size(ETHASH_EPOCH_LENGTH - 1));
	assert_eq!(1082130304usize, get_data_size(ETHASH_EPOCH_LENGTH));
	assert_eq!(1082130304usize, get_data_size(ETHASH_EPOCH_LENGTH + 1));
	assert_eq!(18236833408usize, get_data_size(2046 * ETHASH_EPOCH_LENGTH));
	assert_eq!(18245220736usize, get_data_size(2047 * ETHASH_EPOCH_LENGTH));
}

#[test]
fn test_difficulty_test() {
	let hash = [0xf5, 0x7e, 0x6f, 0x3a, 0xcf, 0xc0, 0xdd, 0x4b, 0x5b, 0xf2, 0xbe, 0xe4, 0x0a, 0xb3, 0x35, 0x8a, 0xa6, 0x87, 0x73, 0xa8, 0xd0, 0x9f, 0x5e, 0x59, 0x5e, 0xab, 0x55, 0x94, 0x05, 0x52, 0x7d, 0x72];
	let mix_hash = [0x1f, 0xff, 0x04, 0xce, 0xc9, 0x41, 0x73, 0xfd, 0x59, 0x1e, 0x3d, 0x89, 0x60, 0xce, 0x6b, 0xdf, 0x8b, 0x19, 0x71, 0x04, 0x8c, 0x71, 0xff, 0x93, 0x7b, 0xb2, 0xd3, 0x2a, 0x64, 0x31, 0xab, 0x6d];
	let nonce = 0xd7b3ac70a301a249;
	let boundary_good = [0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x3e, 0x9b, 0x6c, 0x69, 0xbc, 0x2c, 0xe2, 0xa2, 0x4a, 0x8e, 0x95, 0x69, 0xef, 0xc7, 0xd7, 0x1b, 0x33, 0x35, 0xdf, 0x36, 0x8c, 0x9a, 0xe9, 0x7e, 0x53, 0x84];
	assert_eq!(quick_get_difficulty(&hash, nonce, &mix_hash)[..], boundary_good[..]);
	let boundary_bad = [0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x3a, 0x9b, 0x6c, 0x69, 0xbc, 0x2c, 0xe2, 0xa2, 0x4a, 0x8e, 0x95, 0x69, 0xef, 0xc7, 0xd7, 0x1b, 0x33, 0x35, 0xdf, 0x36, 0x8c, 0x9a, 0xe9, 0x7e, 0x53, 0x84];
	assert!(quick_get_difficulty(&hash, nonce, &mix_hash)[..] != boundary_bad[..]);
}

#[test]
fn test_light_compute() {
	let hash = [0xf5, 0x7e, 0x6f, 0x3a, 0xcf, 0xc0, 0xdd, 0x4b, 0x5b, 0xf2, 0xbe, 0xe4, 0x0a, 0xb3, 0x35, 0x8a, 0xa6, 0x87, 0x73, 0xa8, 0xd0, 0x9f, 0x5e, 0x59, 0x5e, 0xab, 0x55, 0x94, 0x05, 0x52, 0x7d, 0x72];
	let mix_hash = [0x1f, 0xff, 0x04, 0xce, 0xc9, 0x41, 0x73, 0xfd, 0x59, 0x1e, 0x3d, 0x89, 0x60, 0xce, 0x6b, 0xdf, 0x8b, 0x19, 0x71, 0x04, 0x8c, 0x71, 0xff, 0x93, 0x7b, 0xb2, 0xd3, 0x2a, 0x64, 0x31, 0xab, 0x6d];
	let boundary = [0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x3e, 0x9b, 0x6c, 0x69, 0xbc, 0x2c, 0xe2, 0xa2, 0x4a, 0x8e, 0x95, 0x69, 0xef, 0xc7, 0xd7, 0x1b, 0x33, 0x35, 0xdf, 0x36, 0x8c, 0x9a, 0xe9, 0x7e, 0x53, 0x84];
	let nonce = 0xd7b3ac70a301a249;
	// difficulty = 0x085657254bd9u64;
	let light = Light::new(&::std::env::temp_dir(), 486382);
	let result = light_compute(&light, &hash, nonce);
	assert_eq!(result.mix_hash[..], mix_hash[..]);
	assert_eq!(result.value[..], boundary[..]);
}

#[test]
fn test_seed_compute_once() {
	let seed_compute = SeedHashCompute::new();
	let hash = [241, 175, 44, 134, 39, 121, 245, 239, 228, 236, 43, 160, 195, 152, 46, 7, 199, 5, 253, 147, 241, 206, 98, 43, 3, 104, 17, 40, 192, 79, 106, 162];
	assert_eq!(seed_compute.get_seedhash(486382), hash);
}

#[test]
fn test_seed_compute_zero() {
	let seed_compute = SeedHashCompute::new();
	assert_eq!(seed_compute.get_seedhash(0), [0u8; 32]);
}

#[test]
fn test_seed_compute_after_older() {
	let seed_compute = SeedHashCompute::new();
	// calculating an older value first shouldn't affect the result
	let _ = seed_compute.get_seedhash(50000);
	let hash = [241, 175, 44, 134, 39, 121, 245, 239, 228, 236, 43, 160, 195, 152, 46, 7, 199, 5, 253, 147, 241, 206, 98, 43, 3, 104, 17, 40, 192, 79, 106, 162];
	assert_eq!(seed_compute.get_seedhash(486382), hash);
}

#[test]
fn test_seed_compute_after_newer() {
	let seed_compute = SeedHashCompute::new();
	// calculating an newer value first shouldn't affect the result
	let _ = seed_compute.get_seedhash(972764);
	let hash = [241, 175, 44, 134, 39, 121, 245, 239, 228, 236, 43, 160, 195, 152, 46, 7, 199, 5, 253, 147, 241, 206, 98, 43, 3, 104, 17, 40, 192, 79, 106, 162];
	assert_eq!(seed_compute.get_seedhash(486382), hash);
}

#[test]
fn test_drop_old_data() {
	let path = ::std::env::temp_dir();
	let first = Light::new(&path, 0).to_file().unwrap();

	let second = Light::new(&path, ETHASH_EPOCH_LENGTH).to_file().unwrap();
	assert!(fs::metadata(&first).is_ok());

	let _ = Light::new(&path, ETHASH_EPOCH_LENGTH * 2).to_file();
	assert!(fs::metadata(&first).is_err());
	assert!(fs::metadata(&second).is_ok());

	let _ = Light::new(&path, ETHASH_EPOCH_LENGTH * 3).to_file();
	assert!(fs::metadata(&second).is_err());
}