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//! Lowercase hexadecimal formatting via [`fmt::LowerHex`].
use super::U320;
use core::fmt;
/// Formats a [`U320`] as a lowercase hexadecimal string without leading
/// zeros (except for the value zero itself, which formats as `"0"`).
///
/// Supports the `#` alternate flag for a `0x` prefix, matching the
/// standard library convention for integer types.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u320::U320;
///
/// let v = U320::from_be_limbs([0, 0, 0, 0, 255]);
/// assert_eq!(format!("{:x}", v), "ff");
/// assert_eq!(format!("{:#x}", v), "0xff");
/// ```
impl fmt::LowerHex for U320 {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Iterate from MSB (index 4) to LSB (index 0)
let mut first_nonzero = None;
let mut i = 4;
loop {
if self.0[i] != 0 {
first_nonzero = Some(i);
break;
}
if i == 0 {
break;
}
i -= 1;
}
match first_nonzero {
None => {
if f.alternate() {
f.write_str("0x0")
} else {
f.write_str("0")
}
}
Some(idx) => {
if f.alternate() {
f.write_str("0x")?;
}
write!(f, "{:x}", self.0[idx])?;
let mut j = idx;
while j > 0 {
j -= 1;
write!(f, "{:016x}", self.0[j])?;
}
Ok(())
}
}
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Zero formats as "0".
#[test]
fn zero() {
assert_eq!(format!("{:x}", U320::from_be_limbs([0; 5])), "0");
}
/// Zero with alternate flag formats as "0x0".
#[test]
fn zero_alternate() {
assert_eq!(format!("{:#x}", U320::from_be_limbs([0; 5])), "0x0");
}
/// Small value formats without leading zeros.
#[test]
fn small_value() {
let v = U320::from_be_limbs([0, 0, 0, 0, 0xAB]);
assert_eq!(format!("{:x}", v), "ab");
}
/// Value spanning two limbs shows full padding on lower limb.
#[test]
fn two_limbs() {
let v = U320::from_be_limbs([0, 0, 0, 1, 0]);
assert_eq!(format!("{:x}", v), "10000000000000000");
}
/// All-max value fills all 80 hex digits.
#[test]
fn max_value() {
let v = U320::from_be_limbs([u64::MAX; 5]);
let s = format!("{:x}", v);
assert_eq!(s.len(), 80);
assert!(s.chars().all(|c| c == 'f'));
}
/// Alternate flag adds 0x prefix.
#[test]
fn alternate_prefix() {
let v = U320::from_be_limbs([0, 0, 0, 0, 0xCAFE]);
assert_eq!(format!("{:#x}", v), "0xcafe");
}
}