Calculating gas using usize (if supplied gaslimit fits in usize) (#1518)

* Spliting gasometer out of interpreter

* Choosing right gas calculations implementation based on supplied gas

* Moving verification out of gasometer

* MemGasCost benchmark.

Conflicts:
	ethcore/src/evm/benches/mod.rs

* Some simple benchmarks

* Benchmark for simple loop

* Calculating gas_for_memory only when it's actually needed

* Removing superfluous newline [ci skip]

ethcore/src/evm/interpreter/stack.rs

@@ -0,0 +1,106 @@
+// Copyright 2015, 2016 Ethcore (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::fmt;
+use evm::instructions;
+
+/// Stack trait with VM-friendly API
+pub trait Stack<T> {
+	/// Returns `Stack[len(Stack) - no_from_top]`
+	fn peek(&self, no_from_top: usize) -> &T;
+	/// Swaps Stack[len(Stack)] and Stack[len(Stack) - no_from_top]
+	fn swap_with_top(&mut self, no_from_top: usize);
+	/// Returns true if Stack has at least `no_of_elems` elements
+	fn has(&self, no_of_elems: usize) -> bool;
+	/// Get element from top and remove it from Stack. Panics if stack is empty.
+	fn pop_back(&mut self) -> T;
+	/// Get (up to `instructions::MAX_NO_OF_TOPICS`) elements from top and remove them from Stack. Panics if stack is empty.
+	fn pop_n(&mut self, no_of_elems: usize) -> &[T];
+	/// Add element on top of the Stack
+	fn push(&mut self, elem: T);
+	/// Get number of elements on Stack
+	fn size(&self) -> usize;
+	/// Returns all data on stack.
+	fn peek_top(&mut self, no_of_elems: usize) -> &[T];
+}
+
+pub struct VecStack<S> {
+	stack: Vec<S>,
+	logs: [S; instructions::MAX_NO_OF_TOPICS]
+}
+
+impl<S : Copy> VecStack<S> {
+	pub fn with_capacity(capacity: usize, zero: S) -> Self {
+		VecStack {
+			stack: Vec::with_capacity(capacity),
+			logs: [zero; instructions::MAX_NO_OF_TOPICS]
+		}
+	}
+}
+
+impl<S : fmt::Display> Stack<S> for VecStack<S> {
+	fn peek(&self, no_from_top: usize) -> &S {
+		&self.stack[self.stack.len() - no_from_top - 1]
+	}
+
+	fn swap_with_top(&mut self, no_from_top: usize) {
+		let len = self.stack.len();
+		self.stack.swap(len - no_from_top - 1, len - 1);
+	}
+
+	fn has(&self, no_of_elems: usize) -> bool {
+		self.stack.len() >= no_of_elems
+	}
+
+	fn pop_back(&mut self) -> S {
+		let val = self.stack.pop();
+		match val {
+			Some(x) => {
+				evm_debug!({
+					println!("   POP: {}", x)
+				});
+				x
+			},
+			None => panic!("Tried to pop from empty stack.")
+		}
+	}
+
+	fn pop_n(&mut self, no_of_elems: usize) -> &[S] {
+		assert!(no_of_elems <= instructions::MAX_NO_OF_TOPICS);
+
+		for i in 0..no_of_elems {
+			self.logs[i] = self.pop_back();
+		}
+		&self.logs[0..no_of_elems]
+	}
+
+	fn push(&mut self, elem: S) {
+		evm_debug!({
+			println!("  PUSH: {}", elem)
+		});
+		self.stack.push(elem);
+	}
+
+	fn size(&self) -> usize {
+		self.stack.len()
+	}
+
+	fn peek_top(&mut self, no_from_top: usize) -> &[S] {
+		assert!(self.stack.len() >= no_from_top, "peek_top asked for more items than exist.");
+		&self.stack[self.stack.len() - no_from_top .. self.stack.len()]
+	}
+}
+