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use super::*;
fn extract_35_bits(bytes: &[u8]) -> GrainId {
debug_assert!(bytes.len() >= 5);
let value = (bytes[0] as u64) << 27
| (bytes[1] as u64) << 19
| (bytes[2] as u64) << 11
| (bytes[3] as u64) << 3
| (bytes[4] as u64) >> 5;
GrainId::from_u64_lossy(value)
}
impl GrainId {
/// Generate a [`GrainId`] from arbitrary bytes using a fixed-output hash function.
///
/// The first (most significant) 35 bits of the hash output are used to construct the ID.
/// The hash function's output must be at least 5 bytes (40 bits); this is asserted at runtime.
/// All standard cryptographic hash functions satisfy this requirement.
///
/// # Panics
///
/// Panics if the hash function produces fewer than 5 bytes of output.
///
/// # Examples
///
/// ```rust
/// # use grain_id::*;
/// use sha2::Sha256;
///
/// let id = GrainId::from_digest::<Sha256>(b"hello world");
/// // Deterministic: same input always yields same ID.
/// assert_eq!(id, GrainId::from_digest::<Sha256>(b"hello world"));
/// // Different inputs yield different IDs.
/// assert_ne!(id, GrainId::from_digest::<Sha256>(b"goodbye world"));
/// ```
pub fn from_digest<D: ::digest::Digest>(input: &[u8]) -> Self {
let output = D::digest(input);
assert!(
output.len() >= 5,
"digest output is {} bytes, but at least 5 bytes are required",
output.len()
);
extract_35_bits(&output)
}
/// Generate a [`GrainId`] from arbitrary bytes using an extendable-output function (XOF).
///
/// Exactly 5 bytes are read from the XOF output, and the top 35 bits are used to
/// construct the ID.
///
/// # Examples
///
/// ```rust
/// # use grain_id::*;
/// use sha3::Shake128;
///
/// let id = GrainId::from_xof::<Shake128>(b"hello world");
/// // Deterministic: same input always yields same ID.
/// assert_eq!(id, GrainId::from_xof::<Shake128>(b"hello world"));
/// // Different inputs yield different IDs.
/// assert_ne!(id, GrainId::from_xof::<Shake128>(b"goodbye world"));
/// ```
pub fn from_xof<D>(input: &[u8]) -> Self
where
D: ::digest::ExtendableOutput + ::digest::Update + Default,
{
use ::digest::XofReader;
let mut hasher = D::default();
hasher.update(input);
let mut reader = hasher.finalize_xof();
let mut buf = [0u8; 5];
reader.read(&mut buf);
extract_35_bits(&buf)
}
}