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// Copyright 2015-2018 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/>.

use std::sync::Arc;
use hash::KECCAK_EMPTY;
use heapsize::HeapSizeOf;
use ethereum_types::H256;
use parking_lot::Mutex;
use memory_cache::MemoryLruCache;
use bit_set::BitSet;
use super::super::instructions::{self, Instruction};

const DEFAULT_CACHE_SIZE: usize = 4 * 1024 * 1024;

// stub for a HeapSizeOf implementation.
struct Bits(Arc<BitSet>);

impl HeapSizeOf for Bits {
	fn heap_size_of_children(&self) -> usize {
		// dealing in bits here
		self.0.capacity() * 8
	}
}

/// Global cache for EVM interpreter
pub struct SharedCache {
	jump_destinations: Mutex<MemoryLruCache<H256, Bits>>,
}

impl SharedCache {
	/// Create a jump destinations cache with a maximum size in bytes
	/// to cache.
	pub fn new(max_size: usize) -> Self {
		SharedCache {
			jump_destinations: Mutex::new(MemoryLruCache::new(max_size)),
		}
	}

	/// Get jump destinations bitmap for a contract.
	pub fn jump_destinations(&self, code_hash: &H256, code: &[u8]) -> Arc<BitSet> {
		if code_hash == &KECCAK_EMPTY {
			return Self::find_jump_destinations(code);
		}

		if let Some(d) = self.jump_destinations.lock().get_mut(code_hash) {
			return d.0.clone();
		}

		let d = Self::find_jump_destinations(code);
		self.jump_destinations.lock().insert(code_hash.clone(), Bits(d.clone()));

		d
	}

	fn find_jump_destinations(code: &[u8]) -> Arc<BitSet> {
		let mut jump_dests = BitSet::with_capacity(code.len());
		let mut position = 0;

		while position < code.len() {
			let instruction = Instruction::from_u8(code[position]);

			if let Some(instruction) = instruction {
				if instruction == instructions::JUMPDEST {
					jump_dests.insert(position);
				} else if let Some(push_bytes) = instruction.push_bytes() {
					position += push_bytes;
				}
			}
			position += 1;
		}

		jump_dests.shrink_to_fit();
		Arc::new(jump_dests)
	}
}

impl Default for SharedCache {
	fn default() -> Self {
		SharedCache::new(DEFAULT_CACHE_SIZE)
	}
}

#[test]
fn test_find_jump_destinations() {
	use rustc_hex::FromHex;
	// given
	let code = "7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff5b01600055".from_hex().unwrap();

	// when
	let valid_jump_destinations = SharedCache::find_jump_destinations(&code);

	// then
	assert!(valid_jump_destinations.contains(66));
}