From mboxrd@z Thu Jan  1 00:00:00 1970
From: Programmingkid <programmingkidx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [Qemu-devel] [libfdt][PATCH v2] implement strnlen for systems
 that need it
Date: Sun, 22 Oct 2017 15:52:43 -0400
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To: Ian Lepore <ian-h+KGxgPPiopAfugRpC6u6w@public.gmane.org>
Cc: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>, Richard Henderson <richard.henderson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "list-l3A5Bk7waGM@public.gmane.org:PowerPC list:PowerPC" <qemu-ppc-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>, "qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org qemu-devel" <qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>, Peter Maydell <peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>


> On Oct 22, 2017, at 3:06 PM, Ian Lepore <ian-h+KGxgPPiopAfugRpC6u6w@public.gmane.org> wrote:
>=20
> On Sun, 2017-10-22 at 10:41 -0400, Programmingkid wrote:
>>>=20
>>> On Oct 22, 2017, at 1:33 AM, David Gibson  wrote:
>>>=20
>>> On Fri, Oct 20, 2017 at 04:44:58PM -0700, Richard Henderson wrote:
>>>>=20
>>>> On 10/20/2017 10:55 AM, John Arbuckle wrote:
>>>>>=20
>>>>> +static inline size_t strnlen(const char *string, size_t =
max_count)
>>>>> +{
>>>>> +    size_t count;
>>>>> +    for (count =3D 0; count < max_count; count++) {
>>>>> +        if (string[count] =3D=3D '\0') {
>>>>> +            break;
>>>>> +        }
>>>>> +    }
>>>>> +    return count;
>>>> Not to nitpick, but
>>>>=20
>>>>  const char *p =3D memchr(string, 0, max_count);
>>>>  return p ? max_count : p - string;
>>> Richard's right, that's definitely a better implementation.
>> His implementation is smaller, but this one is even smaller. Plus it =
uses the familiar strlen() function:
>>=20
>> size_t strnlen(const char *string, size_t max_count)
>> {
>>     return strlen(string) < max_count ? strlen(string) : max_count;
>> }
>=20
> That is not a proper implementation of strnlen(), which is not =
supposed
> to access any source-string bytes beyond max_count.
>=20
> -- Ian

http://pubs.opengroup.org/onlinepubs/9699919799/functions/strlen.html
This specification document should help anyone who wants more info.

The first implementation using the loop would never access anything =
beyond max_count. My second implementation does go beyond max_count. The =
implementation using memchr() will probably live up the requirement so I =
guess it wins.

Thank you Ian for this information.=20