103 lines
3.7 KiB
Rust
103 lines
3.7 KiB
Rust
//
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// Copyright (c) 2016 KAMADA Ken'ichi.
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions
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// are met:
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// 1. Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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//
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// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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// ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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// SUCH DAMAGE.
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//
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// This is a module to select endianess by using generics
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// in order to avoid run-time dispatching penalty at the cost of
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// increased object size.
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pub trait Endian {
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fn loadu16(buf: &[u8], from: usize) -> u16;
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fn loadu32(buf: &[u8], from: usize) -> u32;
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}
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pub struct BigEndian;
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pub struct LittleEndian;
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macro_rules! generate_load {
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($name:ident, $int_type:ident, $from_func:ident) => (
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fn $name(buf: &[u8], offset: usize) -> $int_type {
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let ptr = (buf.as_ptr() as usize + offset) as *const $int_type;
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let num = unsafe { ::std::mem::transmute(*ptr) };
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$int_type::$from_func(num)
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}
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)
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}
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impl Endian for BigEndian {
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generate_load!(loadu16, u16, from_be);
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generate_load!(loadu32, u32, from_be);
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}
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impl Endian for LittleEndian {
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generate_load!(loadu16, u16, from_le);
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generate_load!(loadu32, u32, from_le);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn loadu16() {
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assert_eq!(BigEndian::loadu16(&[0x01, 0x02], 0), 0x0102);
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assert_eq!(BigEndian::loadu16(&[0x01, 0x02, 0x03], 1), 0x0203);
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assert_eq!(LittleEndian::loadu16(&[0x01, 0x02], 0), 0x0201);
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assert_eq!(LittleEndian::loadu16(&[0x01, 0x02, 0x03], 1), 0x0302);
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}
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#[test]
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fn loadu32() {
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assert_eq!(BigEndian::loadu32(&[0x01, 0x02, 0x03, 0x04], 0),
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0x01020304);
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assert_eq!(BigEndian::loadu32(&[0x01, 0x02, 0x03, 0x04, 0x05], 1),
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0x02030405);
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assert_eq!(LittleEndian::loadu32(&[0x01, 0x02, 0x03, 0x04], 0),
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0x04030201);
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assert_eq!(LittleEndian::loadu32(&[0x01, 0x02, 0x03, 0x04, 0x05], 1),
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0x05040302);
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}
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#[test]
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fn dispatch() {
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fn dispatch_sub<E>(data: &[u8]) -> u16 where E: Endian {
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E::loadu16(data, 0)
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}
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assert_eq!(dispatch_sub::<BigEndian>(&[0x01, 0x02]), 0x0102);
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assert_eq!(dispatch_sub::<LittleEndian>(&[0x01, 0x02]), 0x0201);
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}
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#[test]
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fn static_dispatch() {
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fn dispatch_sub<E>(data: &[u8]) -> u16 where E: Endian {
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E::loadu16(data, 0)
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}
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assert_eq!(dispatch_sub::<BigEndian> as *const (),
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dispatch_sub::<BigEndian> as *const ());
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assert!(dispatch_sub::<BigEndian> as *const () !=
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dispatch_sub::<LittleEndian> as *const ());
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}
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}
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