Differences between function and trait based operation

[chrysn]

Utilizing the crc crate with the crc64::Digest::new(crc64::ECMA) and core::Hasher interface, I was taken aback by the cost of it creating and allocating a table on the stack every time I start a new digest, which is prohibitive in an embedded environment.

The short-hand format checksum_ecma(...) is convenient only as long as data is available in a single run; I had to fall back to defining the field u64 and passing it through update, which is by far not as elegant as using the core::Hasher trait.

As I don't quite understand the reason for the different interfaces, I can make only uninformed suggestions on how the crate's behavior would be better suitable for my needs:

• There could be a slimmer type wrapper around the intermediates that makes the static tables of update() available with a core::Hasher interface.
• The Digest struct could become more general to allow building a Digest that uses the static tables.
• The various two interfaces could be told apart in the README; right now the examples read as if checksum_x25 were just a shorthand for the later crc16::Digest::new(crc16::X25) with write and sum16, while actually it's doing vastly different things performance-wise.

[akhilles]

Please provide feedback on #48. It might address your use cases.

[chrysn]

If v2 is accepted, this can be closed as "fixed by that".