blake3_hasher_init_derive_key_len is an alternative version of
blake3_hasher_init_derive_key which takes the context and its
length as separate parameters, and not together as a C string.
The motivation for this addition is making it easier for
bindings to this C library to call this function without
having to first copy over the context bytes just to add
one 0x00 byte at the end.
Notice that contrary to blake3_hasher_init_derive_key,
blake3_hasher_init_derive_key_len allows the inclusion of a
0x00 byte in the context. Given the rules about context string
selection, this byte is unlikely to be used as part of a context
string. But if for some reason it is ever given, it will be
included in the context string and processed like any other
non-alphanumeric byte would. For compatibility with
blake3_hasher_init_derive_key, bindings should still check for
the absence of 0x00 bytes.
This gives the assembly files the same prefix as the intrinsics files which
simplifies building when the build system should pick between the assembly and
the intrinsics files.
Currently this requires setting the BLAKE3_USE_NEON preprocessor flag.
In the future we may enable this automatically on AArch32/64 or include
some kind of dynamic feature detection. (Though ARM makes this harder
than x86.)
As part of this, get rid of the IS_ARM flag. It wasn't being set
properly when I tried it on a Raspberry Pi.
Closes #30.