Function crypto_generichash 

pub fn crypto_generichash(
    output: &mut [u8],
    input: &[u8],
    key: Option<&[u8]>,
) -> Result<(), Error>

Computes a hash from input and key, copying the result into output.

Parameter	Typical length	Recommended minimum	Accepted lengths
output	CRYPTO_GENERICHASH_BYTES	CRYPTO_GENERICHASH_BYTES_MIN	1 to CRYPTO_GENERICHASH_BYTES_MAX
key	CRYPTO_GENERICHASH_KEYBYTES	CRYPTO_GENERICHASH_KEYBYTES_MIN	0 to CRYPTO_GENERICHASH_KEYBYTES_MAX

As in libsodium, the *_MIN constants are recommendations rather than limits, and an empty key (Some(&[])) computes the same unkeyed hash as None.

Compatible with libsodium’s crypto_generichash.

Errors

Returns an error if the output or key length is outside the accepted range.