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Auto merge of #46919 - michaelwoerister:new-leb128, r=sfackler

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Speed up leb128 encoding and decoding for unsigned values.

Make the implementation for some leb128 functions potentially faster.

@Mark-Simulacrum, could you please trigger a perf.rlo run?
This commit is contained in:
bors 2018-01-20 02:00:13 +00:00
commit 816d765716
2 changed files with 143 additions and 80 deletions
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98
src/libserialize/leb128.rs
View file

@ -9,7 +9,7 @@
// except according to those terms.
#[inline]
fn write_to_vec(vec: &mut Vec<u8>, position: usize, byte: u8) {
pub fn write_to_vec(vec: &mut Vec<u8>, position: usize, byte: u8) {
if position == vec.len() {
vec.push(byte);
} else {
@ -17,25 +17,32 @@ fn write_to_vec(vec: &mut Vec<u8>, position: usize, byte: u8) {
}
}
#[cfg(target_pointer_width = "32")]
const USIZE_LEB128_SIZE: usize = 5;
#[cfg(target_pointer_width = "64")]
const USIZE_LEB128_SIZE: usize = 10;
macro_rules! leb128_size {
(u16) => (3);
(u32) => (5);
(u64) => (10);
(u128) => (19);
(usize) => (USIZE_LEB128_SIZE);
}
macro_rules! impl_write_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => (
#[inline]
/// encodes an integer using unsigned leb128 encoding and stores
/// the result using a callback function.
///
/// The callback `write` is called once for each position
/// that is to be written to with the byte to be encoded
/// at that position.
pub fn write_unsigned_leb128_to<W>(mut value: u128, mut write: W) -> usize
where W: FnMut(usize, u8)
{
let mut position = 0;
loop {
pub fn $fn_name(out: &mut Vec<u8>, start_position: usize, mut value: $int_ty) -> usize {
let mut position = start_position;
for _ in 0 .. leb128_size!($int_ty) {
let mut byte = (value & 0x7F) as u8;
value >>= 7;
if value != 0 {
byte |= 0x80;
}
write(position, byte);
write_to_vec(out, position, byte);
position += 1;
if value == 0 {
@ -43,30 +50,53 @@ pub fn write_unsigned_leb128_to<W>(mut value: u128, mut write: W) -> usize
}
}
position
position - start_position
}
)
}
pub fn write_unsigned_leb128(out: &mut Vec<u8>, start_position: usize, value: u128) -> usize {
write_unsigned_leb128_to(value, |i, v| write_to_vec(out, start_position+i, v))
}
impl_write_unsigned_leb128!(write_u16_leb128, u16);
impl_write_unsigned_leb128!(write_u32_leb128, u32);
impl_write_unsigned_leb128!(write_u64_leb128, u64);
impl_write_unsigned_leb128!(write_u128_leb128, u128);
impl_write_unsigned_leb128!(write_usize_leb128, usize);
macro_rules! impl_read_unsigned_leb128 {
($fn_name:ident, $int_ty:ident) => (
#[inline]
pub fn read_unsigned_leb128(data: &[u8], start_position: usize) -> (u128, usize) {
let mut result = 0;
pub fn $fn_name(slice: &[u8]) -> ($int_ty, usize) {
let mut result: $int_ty = 0;
let mut shift = 0;
let mut position = start_position;
loop {
let byte = data[position];
let mut position = 0;
for _ in 0 .. leb128_size!($int_ty) {
let byte = unsafe {
*slice.get_unchecked(position)
};
position += 1;
result |= ((byte & 0x7F) as u128) << shift;
result |= ((byte & 0x7F) as $int_ty) << shift;
if (byte & 0x80) == 0 {
break;
}
shift += 7;
}
(result, position - start_position)
// Do a single bounds check at the end instead of for every byte.
assert!(position <= slice.len());
(result, position)
}
)
}
impl_read_unsigned_leb128!(read_u16_leb128, u16);
impl_read_unsigned_leb128!(read_u32_leb128, u32);
impl_read_unsigned_leb128!(read_u64_leb128, u64);
impl_read_unsigned_leb128!(read_u128_leb128, u128);
impl_read_unsigned_leb128!(read_usize_leb128, usize);
#[inline]
/// encodes an integer using signed leb128 encoding and stores
@ -130,25 +160,35 @@ pub fn read_signed_leb128(data: &[u8], start_position: usize) -> (i128, usize) {
(result, position - start_position)
}
macro_rules! impl_test_unsigned_leb128 {
($test_name:ident, $write_fn_name:ident, $read_fn_name:ident, $int_ty:ident) => (
#[test]
fn test_unsigned_leb128() {
let mut stream = Vec::with_capacity(10000);
fn $test_name() {
let mut stream = Vec::new();
for x in 0..62 {
let pos = stream.len();
let bytes_written = write_unsigned_leb128(&mut stream, pos, 3 << x);
let bytes_written = $write_fn_name(&mut stream, pos, (3u64 << x) as $int_ty);
assert_eq!(stream.len(), pos + bytes_written);
}
let mut position = 0;
for x in 0..62 {
let expected = 3 << x;
let (actual, bytes_read) = read_unsigned_leb128(&stream, position);
let expected = (3u64 << x) as $int_ty;
let (actual, bytes_read) = $read_fn_name(&stream[position ..]);
assert_eq!(expected, actual);
position += bytes_read;
}
assert_eq!(stream.len(), position);
}
)
}
impl_test_unsigned_leb128!(test_u16_leb128, write_u16_leb128, read_u16_leb128, u16);
impl_test_unsigned_leb128!(test_u32_leb128, write_u32_leb128, read_u32_leb128, u32);
impl_test_unsigned_leb128!(test_u64_leb128, write_u64_leb128, read_u64_leb128, u64);
impl_test_unsigned_leb128!(test_u128_leb128, write_u128_leb128, read_u128_leb128, u128);
impl_test_unsigned_leb128!(test_usize_leb128, write_usize_leb128, read_usize_leb128, usize);
#[test]
fn test_signed_leb128() {

61
src/libserialize/opaque.rs
View file

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use leb128::{read_signed_leb128, read_unsigned_leb128, write_signed_leb128, write_unsigned_leb128};
use leb128::{self, read_signed_leb128, write_signed_leb128};
use std::borrow::Cow;
use std::io::{self, Write};
use serialize;
@ -35,9 +35,9 @@ impl<'a> Encoder<'a> {
macro_rules! write_uleb128 {
($enc:expr, $value:expr) => {{
($enc:expr, $value:expr, $fun:ident) => {{
let pos = $enc.cursor.position() as usize;
let bytes_written = write_unsigned_leb128($enc.cursor.get_mut(), pos, $value as u128);
let bytes_written = leb128::$fun($enc.cursor.get_mut(), pos, $value);
$enc.cursor.set_position((pos + bytes_written) as u64);
Ok(())
}}
@ -55,61 +55,76 @@ macro_rules! write_sleb128 {
impl<'a> serialize::Encoder for Encoder<'a> {
type Error = io::Error;
#[inline]
fn emit_nil(&mut self) -> EncodeResult {
Ok(())
}
#[inline]
fn emit_usize(&mut self, v: usize) -> EncodeResult {
write_uleb128!(self, v)
write_uleb128!(self, v, write_usize_leb128)
}
#[inline]
fn emit_u128(&mut self, v: u128) -> EncodeResult {
write_uleb128!(self, v)
write_uleb128!(self, v, write_u128_leb128)
}
#[inline]
fn emit_u64(&mut self, v: u64) -> EncodeResult {
write_uleb128!(self, v)
write_uleb128!(self, v, write_u64_leb128)
}
#[inline]
fn emit_u32(&mut self, v: u32) -> EncodeResult {
write_uleb128!(self, v)
write_uleb128!(self, v, write_u32_leb128)
}
#[inline]
fn emit_u16(&mut self, v: u16) -> EncodeResult {
write_uleb128!(self, v)
write_uleb128!(self, v, write_u16_leb128)
}
#[inline]
fn emit_u8(&mut self, v: u8) -> EncodeResult {
let _ = self.cursor.write_all(&[v]);
let pos = self.cursor.position() as usize;
leb128::write_to_vec(self.cursor.get_mut(), pos, v);
self.cursor.set_position((pos + 1) as u64);
Ok(())
}
#[inline]
fn emit_isize(&mut self, v: isize) -> EncodeResult {
write_sleb128!(self, v)
}
#[inline]
fn emit_i128(&mut self, v: i128) -> EncodeResult {
write_sleb128!(self, v)
}
#[inline]
fn emit_i64(&mut self, v: i64) -> EncodeResult {
write_sleb128!(self, v)
}
#[inline]
fn emit_i32(&mut self, v: i32) -> EncodeResult {
write_sleb128!(self, v)
}
#[inline]
fn emit_i16(&mut self, v: i16) -> EncodeResult {
write_sleb128!(self, v)
}
#[inline]
fn emit_i8(&mut self, v: i8) -> EncodeResult {
let as_u8: u8 = unsafe { ::std::mem::transmute(v) };
let _ = self.cursor.write_all(&[as_u8]);
Ok(())
self.emit_u8(as_u8)
}
#[inline]
fn emit_bool(&mut self, v: bool) -> EncodeResult {
self.emit_u8(if v {
1
@ -118,20 +133,24 @@ impl<'a> serialize::Encoder for Encoder<'a> {
})
}
#[inline]
fn emit_f64(&mut self, v: f64) -> EncodeResult {
let as_u64: u64 = unsafe { ::std::mem::transmute(v) };
self.emit_u64(as_u64)
}
#[inline]
fn emit_f32(&mut self, v: f32) -> EncodeResult {
let as_u32: u32 = unsafe { ::std::mem::transmute(v) };
self.emit_u32(as_u32)
}
#[inline]
fn emit_char(&mut self, v: char) -> EncodeResult {
self.emit_u32(v as u32)
}
#[inline]
fn emit_str(&mut self, v: &str) -> EncodeResult {
self.emit_usize(v.len())?;
let _ = self.cursor.write_all(v.as_bytes());
@ -140,6 +159,7 @@ impl<'a> serialize::Encoder for Encoder<'a> {
}
impl<'a> Encoder<'a> {
#[inline]
pub fn position(&self) -> usize {
self.cursor.position() as usize
}
@ -162,14 +182,17 @@ impl<'a> Decoder<'a> {
}
}
#[inline]
pub fn position(&self) -> usize {
self.position
}
#[inline]
pub fn set_position(&mut self, pos: usize) {
self.position = pos
}
#[inline]
pub fn advance(&mut self, bytes: usize) {
self.position += bytes;
}
@ -187,10 +210,10 @@ impl<'a> Decoder<'a> {
}
macro_rules! read_uleb128 {
($dec:expr, $t:ty) => ({
let (value, bytes_read) = read_unsigned_leb128($dec.data, $dec.position);
($dec:expr, $t:ty, $fun:ident) => ({
let (value, bytes_read) = leb128::$fun(&$dec.data[$dec.position ..]);
$dec.position += bytes_read;
Ok(value as $t)
Ok(value)
})
}
@ -213,22 +236,22 @@ impl<'a> serialize::Decoder for Decoder<'a> {
#[inline]
fn read_u128(&mut self) -> Result<u128, Self::Error> {
read_uleb128!(self, u128)
read_uleb128!(self, u128, read_u128_leb128)
}
#[inline]
fn read_u64(&mut self) -> Result<u64, Self::Error> {
read_uleb128!(self, u64)
read_uleb128!(self, u64, read_u64_leb128)
}
#[inline]
fn read_u32(&mut self) -> Result<u32, Self::Error> {
read_uleb128!(self, u32)
read_uleb128!(self, u32, read_u32_leb128)
}
#[inline]
fn read_u16(&mut self) -> Result<u16, Self::Error> {
read_uleb128!(self, u16)
read_uleb128!(self, u16, read_u16_leb128)
}
#[inline]
@ -240,7 +263,7 @@ impl<'a> serialize::Decoder for Decoder<'a> {
#[inline]
fn read_usize(&mut self) -> Result<usize, Self::Error> {
read_uleb128!(self, usize)
read_uleb128!(self, usize, read_usize_leb128)
}
#[inline]