Re: [PATCH v4] string.h: Add str_has_prefix() helper function

From: Steven Rostedt
Date: Sat Dec 22 2018 - 22:23:58 EST

On Sun, 23 Dec 2018 12:13:43 +0900
Namhyung Kim <namhyung@xxxxxxxxxx> wrote:

> > Also, I believe there are some memcmp implementations that start at the
> > end of the memory locations, not the beginning. That is, it compares
> > backwards. Which is also legit for memcmp to do.
> I'm not sure, the man page says:
> The memcmp() function returns an integer less than, equal to,
> or greater than zero if the first n bytes of s1 is found,
> respectively, to be less than, to match, or be greater than
> the first n bytes of s2.
> For a nonzero return value, the sign is determined by the sign
> of the difference between the first pair of bytes (interpreted
> as unsigned char) that differ in s1 and s2.
> If n is zero, the return value is zero.
> It should return difference in the first pair of bytes that differ so
> I guess implementations should compare from the beginning.

Ah, makes sense. I think I'm thinking of memcpy() which can start at
the end, or maybe even the deprecated bcmp(). It's been a long time
since I had to deal with the implementations of these.

-- Steve