va_list 0.2.1

Provides a rust implementation of the 'va_list' type for a small set of ABIs. Allowing rust implementations of functions like vprintf.
Documentation 
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/*
 * "cdecl64"
 * Standard stack-based calling convention, with 64-bit aligment
 */
use ::core::{mem,ptr};
use super::VaPrimitive;

const ALIGN: usize = 8;

#[repr(transparent)]
pub struct VaList<'a>(*const u8, ::core::marker::PhantomData<&'a [u64]>);

impl<'a> VaList<'a> {
    // Read a raw value from the list
	// UNSAFE: Doesn't check that the value is POD
    unsafe fn get_raw<T: 'static>(&mut self) -> T {
		// TODO: Advance until type's alignment is met?
        assert_eq!(self.0 as usize % mem::align_of::<T>(), 0);
        let rv = ptr::read(self.0 as *const T);
		// Allow reading under-sized values (always advance by a multiple of 64-bits)
		let slots = (mem::size_of::<T>() + (ALIGN-1)) / ALIGN;
        self.0 = self.0.offset( (slots * ALIGN) as isize );
        rv
    }
}

impl<T: 'static> VaPrimitive for *const T {
    unsafe fn get(list: &mut VaList) -> Self {
		list.get_raw()
    }
}
macro_rules! impl_va_prim {
	( $( $t:ty, )+ ) => {
		$(
			impl VaPrimitive for $t {
				unsafe fn get(l: &mut VaList) -> Self {
					l.get_raw()
				}
			}
		)+
	};
}
impl_va_prim!{
	usize, isize,
	u64, i64,
	u32, i32,
	f64,
	f32,	// f32 will use an entire 64-bit slot
}