Subject: Re: [PATCH 2/2] patch-id: replace `atoi()` with `strtol_i2()`

From: Junio C Hamano <[email-masked]>
Date: Mon, 22 Jan 2024 11:32:36 -0800

"Mohit Marathe via GitGitGadget" <[email-masked]> writes:

>  	static const char digits[] = "0123456789";
>  	const char *q, *r;
> +	char *endp;
>  	int n;
>  
>  	q = p + 4;
>  	n = strspn(q, digits);
>  	if (q[n] == ',') {
>  		q += n + 1;
> -		*p_before = atoi(q);
> +		if (strtol_i2(q, 10, p_before, &endp) != 0)
> +			return 0;
>  		n = strspn(q, digits);
>  	} else {
>  		*p_before = 1;
>  	}

Looking at this code again, because we upfront run strspn() to make
sure q[] begins with a run of digits *and* followed by a comma
(which is not a digit), I think it is safe to use atoi() and assume
it would slurp all the digits.  So the lack of another check the use
of new helper allows us to do, namely

		if (endp != q + n)
			return 0;

is probably OK, but that is one of the two reasons why you would
favor the use of new helper over atoi(), so the upside of this
change is not all that great as I originally hoped for X-<.

Not your fault, of course.  We would still catch when the digit
string that starts q[] is too large to fit in an int, which is an
upside.

> -	if (n == 0 || q[n] != ' ' || q[n+1] != '+')
> +	if (q[n] != ' ' || q[n+1] != '+')
>  		return 0;

When we saw q[] that begins with ',' upon entry to this function, we
used to say *p_before = 1 and then saw n==0 and realized it is not a
good input and returned 0 from the function.

Now we instead peek q[0] and the check says q[0] is not SP so we
will return 0 the same way so there is no behaviour change from the
upper hunk?  The conversion may be correct, but it wasn't explained
in the proposed commit log message.

How are the change to stop caring about n==0 here ...

>  	r = q + n + 2;
>  	n = strspn(r, digits);
>  	if (r[n] == ',') {
>  		r += n + 1;
> -		*p_after = atoi(r);
> -		n = strspn(r, digits);
> +		if (strtol_i2(r, 10, p_after, &endp) != 0)
> +			return 0;
>  	} else {
>  		*p_after = 1;
>  	}
> -	if (n == 0)
> -		return 0;

... and this change here, linked to the switch from atoi() to
strtul_i2()[*]?

It looks like an unrelated behaviour change that is left
unexplained.

>  	return 1;
>  }

Thanks for working on this one.

[Footnote]

 * by the way, what a horrible name for a public function.  Yuck.