rust-bitcoin-unsafe-fast/src/util/endian.rs

macro_rules! define_slice_to_be {
    ($name: ident, $type: ty) => {
        #[inline]
        pub fn $name(slice: &[u8]) -> $type {
            assert_eq!(slice.len(), ::std::mem::size_of::<$type>());
            let mut res = 0;
            for i in 0..::std::mem::size_of::<$type>() {
                res |= (slice[i] as $type) << (::std::mem::size_of::<$type>() - i - 1)*8;
            }
            res
        }
    }
}
macro_rules! define_slice_to_le {
    ($name: ident, $type: ty) => {
        #[inline]
        pub fn $name(slice: &[u8]) -> $type {
            assert_eq!(slice.len(), ::std::mem::size_of::<$type>());
            let mut res = 0;
            for i in 0..::std::mem::size_of::<$type>() {
                res |= (slice[i] as $type) << i*8;
            }
            res
        }
    }
}
macro_rules! define_be_to_array {
    ($name: ident, $type: ty, $byte_len: expr) => {
        #[inline]
        pub fn $name(val: $type) -> [u8; $byte_len] {
            assert_eq!(::std::mem::size_of::<$type>(), $byte_len); // size_of isn't a constfn in 1.22
            let mut res = [0; $byte_len];
            for i in 0..$byte_len {
                res[i] = ((val >> ($byte_len - i - 1)*8) & 0xff) as u8;
            }
            res
        }
    }
}
macro_rules! define_le_to_array {
    ($name: ident, $type: ty, $byte_len: expr) => {
        #[inline]
        pub fn $name(val: $type) -> [u8; $byte_len] {
            assert_eq!(::std::mem::size_of::<$type>(), $byte_len); // size_of isn't a constfn in 1.22
            let mut res = [0; $byte_len];
            for i in 0..$byte_len {
                res[i] = ((val >> i*8) & 0xff) as u8;
            }
            res
        }
    }
}

define_slice_to_be!(slice_to_u32_be, u32);
define_be_to_array!(u32_to_array_be, u32, 4);
define_slice_to_le!(slice_to_u16_le, u16);
define_slice_to_le!(slice_to_u32_le, u32);
define_slice_to_le!(slice_to_u64_le, u64);
define_le_to_array!(u16_to_array_le, u16, 2);
define_le_to_array!(u32_to_array_le, u32, 4);
define_le_to_array!(u64_to_array_le, u64, 8);

#[inline]
pub fn i16_to_array_le(val: i16) -> [u8; 2] {
    u16_to_array_le(val as u16)
}
#[inline]
pub fn slice_to_i16_le(slice: &[u8]) -> i16 {
    slice_to_u16_le(slice) as i16
}
#[inline]
pub fn slice_to_i32_le(slice: &[u8]) -> i32 {
    slice_to_u32_le(slice) as i32
}
#[inline]
pub fn i32_to_array_le(val: i32) -> [u8; 4] {
    u32_to_array_le(val as u32)
}
#[inline]
pub fn slice_to_i64_le(slice: &[u8]) -> i64 {
    slice_to_u64_le(slice) as i64
}
#[inline]
pub fn i64_to_array_le(val: i64) -> [u8; 8] {
    u64_to_array_le(val as u64)
}

macro_rules! define_chunk_slice_to_int {
    ($name: ident, $type: ty, $converter: ident) => {
        #[inline]
        pub fn $name(inp: &[u8], outp: &mut [$type]) {
            assert_eq!(inp.len(), outp.len() * ::std::mem::size_of::<$type>());
            for (outp_val, data_bytes) in outp.iter_mut().zip(inp.chunks(::std::mem::size_of::<$type>())) {
                *outp_val = $converter(data_bytes);
            }
        }
    }
}
define_chunk_slice_to_int!(bytes_to_u64_slice_le, u64, slice_to_u64_le);

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn endianness_test() {
        assert_eq!(slice_to_u32_be(&[0xde, 0xad, 0xbe, 0xef]), 0xdeadbeef);
        assert_eq!(u32_to_array_be(0xdeadbeef), [0xde, 0xad, 0xbe, 0xef]);

        assert_eq!(slice_to_u16_le(&[0xad, 0xde]), 0xdead);
        assert_eq!(slice_to_u32_le(&[0xef, 0xbe, 0xad, 0xde]), 0xdeadbeef);
        assert_eq!(slice_to_u64_le(&[0xef, 0xbe, 0xad, 0xde, 0xfe, 0xca, 0xad, 0x1b]), 0x1badcafedeadbeef);
        assert_eq!(u16_to_array_le(0xdead), [0xad, 0xde]);
        assert_eq!(u32_to_array_le(0xdeadbeef), [0xef, 0xbe, 0xad, 0xde]);
        assert_eq!(u64_to_array_le(0x1badcafedeadbeef), [0xef, 0xbe, 0xad, 0xde, 0xfe, 0xca, 0xad, 0x1b]);
    }

    #[test]
    fn endian_chunk_test() {
        let inp = [0xef, 0xbe, 0xad, 0xde, 0xfe, 0xca, 0xad, 0x1b, 0xfe, 0xca, 0xad, 0x1b, 0xce, 0xfa, 0x01, 0x02];
        let mut out = [0; 2];
        bytes_to_u64_slice_le(&inp, &mut out);
        assert_eq!(out, [0x1badcafedeadbeef, 0x0201face1badcafe]);
    }
}