hash: Use size_t instead of int for RFC6979 outlen copy

[john-moffett]

If outlen > INT_MAX it results in segfault or hang (when outlen is a multiple of 2^32) on most implementations due to conversion in: int now = outlen producing negative values or zero. Unreachable in current code and highly improbable in future practice, but fits contract better and fixes a couple of compiler warnings.

[fanquake]

fixes a couple of compiler warnings

Which compiler / warnings?

[john-moffett]

Not with default flags. I used clang -Wimplicit-int-conversion -Wshorten-64-to-32. It'd probably show up with gcc -Wconversion. There are a lot of benign warnings, but this one stood out to me.

[real-or-random]

If you want to improve this further, I'd suggest

• renaming now to chunk_len (consistency with the SHA256 implementation above)
• moving the entire if block just below the initialization of now (or chunk_len). (The goal is to compute max(outlen, 32). Spreading this over two blocks is a bit silly. It's probably a result of the C89 rule that declarations need to be at the beginning of a block. edit: Indeed, see 792bcdb#diff-e91b67aa33d606267c28ce5da48a89cc789f4081c176eb581a9bff780afd1d6cR260-L262 )

[john-moffett]

Thanks! I'll hold off for the moment. Hopefully it'll inspire someone to replace this nonce generation process with something more lightweight and straightforward like BIP340's approach. :)

[real-or-random]

utACK 960ba5f

Thanks a lot! Consistency of integer types is indeed a bit of a weak spot, at least in the old parts of the library code.

[theStack]

Code-review ACK 960ba5f