pub(crate) type Digit = u64;
pub(crate) type DoubleDigit = u128;
pub(crate) const BYTES: usize = 8;
pub(crate) const BITS: usize = BYTES * 8;
pub(crate) fn from_bytes_be(bytes: &[u8]) -> Vec<Digit> {
if bytes.is_empty() {
return Vec::new();
}
let mut digits = Vec::with_capacity(bytes.len().div_ceil(8));
for chunk in bytes.rchunks(8) {
if chunk.len() == 8 {
let arr: [u8; 8] = unsafe { chunk.try_into().unwrap_unchecked() };
digits.push(Digit::from_be_bytes(arr));
} else {
let mut val = 0;
for &b in chunk {
val = (val << 8) | b as Digit;
}
digits.push(val);
}
}
digits
}
pub(crate) fn div_rem255(num: &mut Vec<Digit>) -> u8 {
let mut rem = 0u64;
for d in num.iter_mut().rev() {
let (sum_low, overflow) = d.overflowing_add(rem);
if !overflow {
*d = rem * 0x0101010101010101 + sum_low / 255;
rem = sum_low % 255;
} else {
*d = (rem + 1) * 0x0101010101010101;
rem = sum_low + 1;
}
}
while num.len() > 1 && unsafe { *num.get_unchecked(num.len() - 1) == 0 } {
num.pop();
}
rem as u8
}