[WASM] mem_cmp added to the Wasm runtime

ethcore/vm/src/schedule.rs

@@ -128,6 +128,8 @@ pub struct WasmCosts {
 	/// Memory (load/store) operations multiplier.
 	pub mem: u32,
 	/// Memory copy operation, per byte.
+	pub mem_cmp: u32,
+	/// Memory copy operation, per byte.
 	pub mem_copy: u32,
 	/// Memory move operation, per byte.
 	pub mem_move: u32,
@@ -148,6 +150,7 @@ impl Default for WasmCosts {
 			div: 16,
 			mul: 4,
 			mem: 2,
+			mem_cmp: 1,
 			mem_copy: 1,
 			mem_move: 1,
 			mem_set: 1,

ethcore/wasm/Cargo.toml

@@ -8,6 +8,7 @@ byteorder = "1.0"
 ethereum-types = "0.1"
 log = "0.3"
 parity-wasm = "0.15"
+libc = "0.2"
 wasm-utils = { git = "https://github.com/paritytech/wasm-utils" }
 vm = { path = "../vm" }
 ethcore-logger = { path = "../../logger" }

ethcore/wasm/src/env.rs

@@ -92,6 +92,11 @@ pub const SIGNATURES: &'static [UserFunctionDescriptor] = &[
 		&[I32; 3],
 		Some(I32),
 	),
+	Static(
+		"_ext_memcmp",
+		&[I32; 3],
+		Some(I32),
+	),
 	Static(
 		"_ext_memcpy",
 		&[I32; 3],

ethcore/wasm/src/lib.rs

@@ -22,6 +22,7 @@ extern crate ethereum_types;
 extern crate ethcore_logger;
 extern crate byteorder;
 extern crate parity_wasm;
+extern crate libc;
 extern crate wasm_utils;
 
 mod runtime;

ethcore/wasm/src/runtime.rs

@@ -19,6 +19,7 @@
 use std::sync::Arc;
 
 use byteorder::{LittleEndian, ByteOrder};
+use libc::{memcmp, c_void};
 
 use vm;
 use panic_payload;
@@ -567,6 +568,28 @@ impl<'a, 'b> Runtime<'a, 'b> {
 		&*self.memory
 	}
 
+	fn mem_cmp(&mut self, context: InterpreterCallerContext)
+		-> Result<Option<interpreter::RuntimeValue>, InterpreterError>
+	{
+		//
+		// method signature:
+		//   fn memcmp(cx: *const u8, ct: *const u8, n: usize) -> i32;
+		//
+
+		let len = context.value_stack.pop_as::<i32>()? as u32;
+		let cx = context.value_stack.pop_as::<i32>()? as u32;
+		let ct = context.value_stack.pop_as::<i32>()? as u32;
+
+		self.charge(|schedule| schedule.wasm.mem_cmp as u64 * len as u64)?;
+
+		let cx = self.memory.get(cx, len as usize)?;
+		let ct = self.memory.get(ct, len as usize)?;
+		let result = unsafe {
+			memcmp(cx.as_ptr() as *const c_void, ct.as_ptr() as *const c_void, len as usize)
+		};
+		Ok(Some(Into::into(result)))
+	}
+
 	fn mem_copy(&mut self, context: InterpreterCallerContext)
 		-> Result<Option<interpreter::RuntimeValue>, InterpreterError>
 	{
@@ -890,6 +913,9 @@ impl<'a, 'b> interpreter::UserFunctionExecutor<UserTrap> for Runtime<'a, 'b> {
 			"_emscripten_memcpy_big" => {
 				self.mem_copy(context)
 			},
+			"_ext_memcmp" => {
+				self.mem_cmp(context)
+			},
 			"_ext_memcpy" => {
 				self.mem_copy(context)
 			},