Re: [PATCH 2/4] avoid computing zero offsets from NULL pointer

> switch to iterating with a numeric index (as we do in sequencer.c here).
> In other cases (like the cache_end one) the use of an end pointer is
> more natural; we can keep that by just explicitly checking for NULL when
> assigning the end pointer.
>
> diff --git a/xdiff-interface.c b/xdiff-interface.c
> index 8509f9ea22..2f1fe48512 100644
> --- a/xdiff-interface.c
> +++ b/xdiff-interface.c
> @@ -84,8 +84,8 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b)
>  {
>  	const int blk = 1024;
>  	long trimmed = 0, recovered = 0;
> -	char *ap = a->ptr + a->size;
> -	char *bp = b->ptr + b->size;
> +	char *ap = a->ptr ? a->ptr + a->size : a->ptr;
> +	char *bp = b->ptr ? b->ptr + b->size : b->ptr;
>  	long smaller = (a->size < b->size) ? a->size : b->size;
>  
>  	while (blk + trimmed <= smaller && !memcmp(ap - blk, bp - blk, blk)) {