From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Thu, 21 Sep 2017 07:42:35 GMT
Subject: Re: [PATCH v2 02/21] prefix_ref_iterator: break when we leave the prefix
Message-ID: <32b3d338-6781-a600-2c7e-65dc2818aab5@alum.mit.edu>
In-Reply-To: <CAGZ79kbwCAidGR3cgukdjckZVYwj+qbOikqN-e934uP1yk9Cuw@mail.gmail.com>

On 09/20/2017 10:25 PM, Stefan Beller wrote:
> On Mon, Sep 18, 2017 at 11:22 PM, Michael Haggerty <mhagger@alum.mit.edu> wrote:
>> [...]
>> +/* Return -1, 0, 1 if refname is before, inside, or after the prefix. */
>> +static int compare_prefix(const char *refname, const char *prefix)
>> +{
>> +       while (*prefix) {
>> +               if (*refname != *prefix)
>> +                       return ((unsigned char)*refname < (unsigned char)*prefix) ? -1 : +1;
> 
> This looks interesting.
> 
> We get a signed char* , cast it to unsigned char* and then
> compare byte by byte.

Not quite. We get a `char *` of unknown signedness (it's
implementation-dependent), dereference it into a `char`, then cast that
value to `unsigned char`. What you described would be

    *(const unsigned char *)refname < *(const unsigned char *)prefix

But I assume that these two variants would result in identical assembly
code.

> [...]

Michael