phc-discussions - Re: [PHC] Specification of a modular crypt format (2)

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Message-ID: <20151009121815.GA22236@bolet.org>
Date: Fri, 9 Oct 2015 14:18:15 +0200
From: Thomas Pornin <pornin@...et.org>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Specification of a modular crypt format (2)

On Fri, Oct 09, 2015 at 04:16:58AM +0300, Alexander Cherepanov wrote:
> inline is not in C89.

This is true. I'll fix it.

> Such casts are probably for C++ compatibility...

Exactly. Though I want to write portable C code, I'd prefer it if this
code can also be used "as is" in C++, because I know that there are a
lot of developers out there who think in terms of "C/C++" without really
noticing that they are distinct languages.

> >		acc = (acc << 6) + (unsigned)d;
> 
> ...but this one seems entirely redundant:-)

This cast is for readability. Readability depends on who is doing the
reading, and, in this case, the cast is for me. I tend to add explicit
casts when switching between signed and unsigned integer types, because
long ago I ran into trouble with signedness issues(*) and I got into the
habit of making things more obvious.

The cast is redundant because the C compiler already applies it -- so
the compiler won't mind.

(*) This code:

	unsigned x = 10;
	long y = -1;
	if (x < y) {
		...
	}

will execute the code in the 'if' on a 32-bit machine, not on a 64-bit
machine(**); and this is not undefined behaviour. In both cases, the
result is clearly and unambiguously defined by the standard.

(**) Except on Windows / Visual C with default option on 64-bit Windows,
where 'long' is still 32-bit for compatibility with existing code and
API that equates 'DWORD' with 'unsigned long'.

	--Thomas