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//! Conversion from [`U320`] into a `[u8; 40]` big-endian byte array.
use super::U320;
/// Converts a [`U320`] into a 40-byte array in big-endian order where
/// byte `[0]` is the most significant and byte `[39]` is the least
/// significant.
///
/// This is the inverse of [`U320::from_be_bytes`]. Each of the five
/// `u64` limbs is serialized via `u64::to_be_bytes` into the
/// corresponding 8-byte slice, reading from MSB (index 4) down.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u320::U320;
///
/// let v = U320::from_be_limbs([0, 0, 0, 0, 1]);
/// let bytes: [u8; 40] = v.into();
/// assert_eq!(bytes[39], 1);
/// assert_eq!(bytes[0], 0);
/// ```
impl From<U320> for [u8; 40] {
#[inline]
fn from(value: U320) -> Self {
let w0 = value.0[4].to_be_bytes();
let w1 = value.0[3].to_be_bytes();
let w2 = value.0[2].to_be_bytes();
let w3 = value.0[1].to_be_bytes();
let w4 = value.0[0].to_be_bytes();
[
w0[0], w0[1], w0[2], w0[3], w0[4], w0[5], w0[6], w0[7],
w1[0], w1[1], w1[2], w1[3], w1[4], w1[5], w1[6], w1[7],
w2[0], w2[1], w2[2], w2[3], w2[4], w2[5], w2[6], w2[7],
w3[0], w3[1], w3[2], w3[3], w3[4], w3[5], w3[6], w3[7],
w4[0], w4[1], w4[2], w4[3], w4[4], w4[5], w4[6], w4[7],
]
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Round-trip: from_be_bytes then into bytes returns the original.
#[test]
fn round_trip() {
let mut bytes = [0u8; 40];
bytes[0] = 0xAB;
bytes[19] = 0xCD;
bytes[39] = 0xEF;
let v = U320::from_be_bytes(bytes);
let back: [u8; 40] = v.into();
assert_eq!(back, bytes);
}
/// Zero produces all-zero bytes.
#[test]
fn zero() {
let bytes: [u8; 40] = U320::ZERO.into();
assert_eq!(bytes, [0u8; 40]);
}
/// MAX produces all-0xFF bytes.
#[test]
fn max() {
let bytes: [u8; 40] = U320::MAX.into();
assert_eq!(bytes, [0xFF; 40]);
}
/// Byte 39 holds the LSB of the lowest limb.
#[test]
fn lsb_position() {
let v = U320::from_be_limbs([0, 0, 0, 0, 0x42]);
let bytes: [u8; 40] = v.into();
assert_eq!(bytes[39], 0x42);
assert_eq!(bytes[38], 0);
}
/// Byte 0 holds the MSB of the highest limb.
#[test]
fn msb_position() {
let v = U320::from_be_limbs([0xAB00000000000000, 0, 0, 0, 0]);
let bytes: [u8; 40] = v.into();
assert_eq!(bytes[0], 0xAB);
assert_eq!(bytes[1], 0);
}
}