Hashers take a stream of bytes (of arbitrary length) and produce a fixed length value - the hash. For example, the CRC-32/IEEE hashing algorithm produces a 32 bit value (a base.u32). The MD5 hashing algorithm produces a 128 bit value.
Wuffs' hasher implementations have one core method. For 32 bit hashes, the method signature is update_u32!(x: roslice base.u8) base.u32. It incrementally updates the hasher object's state with the addition data x, and returns the hash value so far, for all of the data up to and including x.
This method is stateful. Calling update_u32 twice with the same slice of bytes can produce two different hash values. Conversely, calling update_u32 twice with two different slices should be equivalent to calling it once on their concatenation. Re-initialize the object to reset the state.
The update_u32! method is equivalent to calling update! and then checksum_u32 (which is a pure method). For the rare algorithms where computing the checksum from internal state is relatively expensive, and when streaming many relatively-small updates, it might be more efficient to call update! N times and checksum_u32 only once, instead of calling update_u32! N times.
Wuffs' hasher implementations are not cryptographic. They make no attempt to resist timing attacks.
In Wuffs syntax, the base.hasher_u32 methods are:
checksum_u32() u32get_quirk(key: u32) u64set_quirk!(key: u32, value: u64) statusupdate!(x: slice u8)update_u32!(x: slice u8) u32The base.hasher_u64 and base.hasher_bitvec256 methods are similar, except for the obvious difference of calculating a 64-bit or 256-bit (not 32-bit) checksum.
See also the general remarks on Wuffs' standard library.