Efficient lookup by zero-terminated C string

[gsnoff]

In some use cases (like returning a pointer by a symbol in FFI scenario) it is needed to look up a value by a given *const c_char, without assuming anything about the encoding except that a single NUL byte always ends the sequence. In this regard it could be similar to a binary lookup, but without having the length of the input sequence as an immediate value beforehand.

Is it reasonable to provide a specialized routine for incremental comparison to save cycles by not performing the length count in a separate pass?

[sfackler]

It seems like you can have the PhfHash implementation take care of looking for the null terminator as it's hashing?

[abonander]

We could implement PhfHash and FmtConst for CStr now.

[abonander]

Thinking about this more, I'm not sure if hiding the unsafety of looking for a \0 behind a raw pointer is worth saving an extra scan of the string since the initial length finding will bring it into cache anyway.

[gsnoff]

@abonander The unsafety can be dealt with in strncmp-esque manner, by having a wrapper type with both a c_char pointer and a maximum length, not actual length. (A slice might work here too, I guess? It’s the semantics of stopping at null character that’s important, anyway.)

And I think the caching might not always work as intended in low-end embedded environments such as Cortex-M0. Individual cycles can be pretty expensive there, especially in real-time tasks.