Solitaire
Bruce Schneier's Solitaire algorithm, as described in Neil Stephenson's Cryptonomicon.
Overview
Solitaire is a crypto algorithm which uses permutations of a fairly standard deck of cards to generate a stream of pseudo-random alphabetical characters, which can be added to an input message to encrypt it.
Implementation details
This implementation uses a standard array to store the cards. I considered basing this on alloc::collections::LinkedList and its CursorMut implementation instead, because it seemed like fun and could make cut operations much more performant. I chose not to for two reasons:
- Searching through a slice is much faster than searching through a linked list: LLs trash the processor cache, where slices utilize it efficiently. Searching is a common operation in this algorithm.
- As each card takes 1 byte, a 54-card deck is actually pretty small. Structs this size are declared
Copyall the time; it seems likely that it would be actually faster to just re-copy the array as required instead of messing around with list pointer manipulation optimizations.
The textbyte package uses a lot of trait objects, the consequence of which is that there's some indirection on function invocation for its traits. That's probably fine; in most cases, each of those functions will be called only a very few times for any given program execution, so they shouldn't represent an appreciable slowdown. While it's possible to work around that with a different design, the usage pattern is a lot uglier: nested function calls instead of call chains.