Re: [PATCH 3/4] cache.h: hex2chr() - avoid -Wsign-compare warnings
- From
Jeff King <peff@peff.net>
- Date
- Sep 22, 2017, 05:47 UTC
- Message-ID
- <20170922054748.iseinawwwfw56vis@sigill.intra.peff.net>
- In-Reply-To
- <ae537e7e-2c3d-f7f3-28f4-451c37c01bbb@ramsayjones.plus.com>
On Thu, Sep 21, 2017 at 05:48:38PM +0100, Ramsay Jones wrote:
Show 13 quoted lines
> diff --git a/cache.h b/cache.h
> index a916bc79e..a0e3e362c 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -1243,8 +1243,8 @@ static inline unsigned int hexval(unsigned char c)
> */
> static inline int hex2chr(const char *s)
> {
> - int val = hexval(s[0]);
> - return (val < 0) ? val : (val << 4) | hexval(s[1]);
> + unsigned int val = hexval(s[0]);
> + return (val & ~0xf) ? val : (val << 4) | hexval(s[1]);
> }Ironically, the unsigned return from hexval() comes from internally converting the signed char in hexval_table. And then we again return it as a signed int from hex2chr().
Would it make sense to return a signed int from hexval()? That would make hex2chr just work as it tries to above. I admit that shifting signed values is a little funny, but it should be fine here since we know they're no larger than 8 bits in the first place.
As an aside, I also see some uses of hexval() that don't appear to be quite as rigorous in checking for invalid characters. A few unconditionally shift the first nibble and assume that there will still be high bits set. I think that's generally true for twos-complement negative numbers, but isn't shifting off the left side of a signed integer undefined behavior?
And mailinfo's decode_q_segment() does not seem to check for errors at all.
Handling those is getting far off your original patch, but I'm having trouble figuring out if it's saner for us to consistently stick to all-signed or all-unsigned here.
-Peff