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optimise ReadBytes #17

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optimise ReadBytes #17

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98 changes: 80 additions & 18 deletions src/input.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@

use std::cmp;
use std::io;
use std::mem;

/// Similar to `std::io::BufRead`, but more performant.
///
Expand Down Expand Up @@ -66,6 +67,62 @@ impl<R: io::Read> BufferedReader<R> {
}
}

/// Aligned 16-bit buffer and converter
#[derive(Copy, Clone)]
#[repr(align(2))]
struct Helper16([u8; 2]);

/// Aligned 32-bit buffer and converter
#[derive(Copy, Clone)]
#[repr(align(4))]
struct Helper32([u8; 4]);

/// Aligned 64-bit buffer and converter
#[derive(Copy, Clone)]
#[repr(align(8))]
struct Helper64([u8; 8]);

impl Helper16 {
/// Transmute aligned little-endian buffer to integer
#[allow(dead_code)]
#[inline(always)]
pub fn to_u16_le(self) -> u16 {
u16::from_le(unsafe { mem::transmute::<[u8; 2], u16>(self.0) })
}
/// Transmute aligned big-endian buffer to integer
#[inline(always)]
pub fn to_u16_be(self) -> u16 {
u16::from_be(unsafe { mem::transmute::<[u8; 2], u16>(self.0) })
}
}

impl Helper32 {
/// Transmute aligned little-endian buffer to integer
#[inline(always)]
pub fn to_u32_le(self) -> u32 {
u32::from_le(unsafe { mem::transmute::<[u8; 4], u32>(self.0) })
}
/// Transmute aligned big-endian buffer to integer
#[inline(always)]
pub fn to_u32_be(self) -> u32 {
u32::from_be(unsafe { mem::transmute::<[u8; 4], u32>(self.0) })
}
}

impl Helper64 {
/// Transmute aligned little-endian buffer to integer
#[allow(dead_code)]
#[inline(always)]
pub fn to_u64_le(self) -> u64 {
u64::from_le(unsafe { mem::transmute::<[u8; 8], u64>(self.0) })
}
/// Transmute aligned big-endian buffer to integer
#[allow(dead_code)]
#[inline(always)]
pub fn to_u64_be(self) -> u64 {
u64::from_be(unsafe { mem::transmute::<[u8; 8], u64>(self.0) })
}
}

/// Provides convenience methods to make input less cumbersome.
pub trait ReadBytes {
Expand All @@ -85,45 +142,50 @@ pub trait ReadBytes {

/// Reads two bytes and interprets them as a big-endian 16-bit unsigned integer.
fn read_be_u16(&mut self) -> io::Result<u16> {
let b0 = try!(self.read_u8()) as u16;
let b1 = try!(self.read_u8()) as u16;
Ok(b0 << 8 | b1)
Ok(Helper16([
try!(self.read_u8()),
try!(self.read_u8()),
]).to_u16_be())
}

/// Reads two bytes and interprets them as a big-endian 16-bit unsigned integer.
fn read_be_u16_or_eof(&mut self) -> io::Result<Option<u16>> {
if let Some(b0) = try!(self.read_u8_or_eof()) {
if let Some(b1) = try!(self.read_u8_or_eof()) {
return Ok(Some((b0 as u16) << 8 | (b1 as u16)));
return Ok(Some(Helper16([b0, b1]).to_u16_be()));
}
}
Ok(None)
}

/// Reads three bytes and interprets them as a big-endian 24-bit unsigned integer.
fn read_be_u24(&mut self) -> io::Result<u32> {
let b0 = try!(self.read_u8()) as u32;
let b1 = try!(self.read_u8()) as u32;
let b2 = try!(self.read_u8()) as u32;
Ok(b0 << 16 | b1 << 8 | b2)
Ok(Helper32([
0,
try!(self.read_u8()),
try!(self.read_u8()),
try!(self.read_u8()),
]).to_u32_be())
}

/// Reads four bytes and interprets them as a big-endian 32-bit unsigned integer.
fn read_be_u32(&mut self) -> io::Result<u32> {
let b0 = try!(self.read_u8()) as u32;
let b1 = try!(self.read_u8()) as u32;
let b2 = try!(self.read_u8()) as u32;
let b3 = try!(self.read_u8()) as u32;
Ok(b0 << 24 | b1 << 16 | b2 << 8 | b3)
Ok(Helper32([
try!(self.read_u8()),
try!(self.read_u8()),
try!(self.read_u8()),
try!(self.read_u8()),
]).to_u32_be())
}

/// Reads four bytes and interprets them as a little-endian 32-bit unsigned integer.
fn read_le_u32(&mut self) -> io::Result<u32> {
let b0 = try!(self.read_u8()) as u32;
let b1 = try!(self.read_u8()) as u32;
let b2 = try!(self.read_u8()) as u32;
let b3 = try!(self.read_u8()) as u32;
Ok(b3 << 24 | b2 << 16 | b1 << 8 | b0)
Ok(Helper32([
try!(self.read_u8()),
try!(self.read_u8()),
try!(self.read_u8()),
try!(self.read_u8()),
]).to_u32_le())
}
}

Expand Down