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//! Construction of a [`U384`] from a 48-byte big-endian array.
use super::U384;
impl U384 {
/// Creates a new [`U384`] from a 48-byte array in big-endian order.
///
/// Bytes `[0..8]` become limb `w0` (most significant), bytes `[8..16]`
/// become `w1`, and so on through bytes `[40..48]` which become `w5`
/// (least significant).
///
/// # Examples
///
/// ```
/// use cnfy_uint::u384::U384;
///
/// let mut bytes = [0u8; 48];
/// bytes[47] = 1;
/// assert_eq!(U384::from_be_bytes(bytes), U384::from_be_limbs([0, 0, 0, 0, 0, 1]));
/// ```
#[inline]
pub const fn from_be_bytes(bytes: [u8; 48]) -> Self {
let w0 = u64::from_be_bytes([
bytes[0], bytes[1], bytes[2], bytes[3], bytes[4], bytes[5], bytes[6], bytes[7],
]);
let w1 = u64::from_be_bytes([
bytes[8], bytes[9], bytes[10], bytes[11], bytes[12], bytes[13], bytes[14], bytes[15],
]);
let w2 = u64::from_be_bytes([
bytes[16], bytes[17], bytes[18], bytes[19], bytes[20], bytes[21], bytes[22], bytes[23],
]);
let w3 = u64::from_be_bytes([
bytes[24], bytes[25], bytes[26], bytes[27], bytes[28], bytes[29], bytes[30], bytes[31],
]);
let w4 = u64::from_be_bytes([
bytes[32], bytes[33], bytes[34], bytes[35], bytes[36], bytes[37], bytes[38], bytes[39],
]);
let w5 = u64::from_be_bytes([
bytes[40], bytes[41], bytes[42], bytes[43], bytes[44], bytes[45], bytes[46], bytes[47],
]);
Self([w5, w4, w3, w2, w1, w0])
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// All zeros produces the zero value.
#[test]
fn zero() {
assert_eq!(
U384::from_be_bytes([0; 48]),
U384::from_be_limbs([0, 0, 0, 0, 0, 0]),
);
}
/// All 0xFF produces the maximum value.
#[test]
fn max() {
assert_eq!(
U384::from_be_bytes([0xFF; 48]),
U384::MAX,
);
}
/// Byte 47 (least significant) maps to the low bit of limb w5.
#[test]
fn single_lsb() {
let mut bytes = [0u8; 48];
bytes[47] = 1;
assert_eq!(
U384::from_be_bytes(bytes),
U384::from_be_limbs([0, 0, 0, 0, 0, 1]),
);
}
/// Byte 0 (most significant) maps to the high bit of limb w0.
#[test]
fn single_msb() {
let mut bytes = [0u8; 48];
bytes[0] = 0x80;
assert_eq!(
U384::from_be_bytes(bytes),
U384::from_be_limbs([0x8000000000000000, 0, 0, 0, 0, 0]),
);
}
/// Boundary between w2 and w3 at bytes 23/24.
#[test]
fn limb_boundary() {
let mut bytes = [0u8; 48];
bytes[23] = 1;
bytes[24] = 1;
assert_eq!(
U384::from_be_bytes(bytes),
U384::from_be_limbs([0, 0, 1, 0x0100000000000000, 0, 0]),
);
}
}