Re: [RFC PATCH 02/10] range-diff.c: don't use st_mult() for signed "int"

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Peff,

On Fri, 10 Dec 2021, Jeff King wrote:

> On Fri, Dec 10, 2021 at 11:22:59AM +0100, Ævar Arnfjörð Bjarmason wrote:
>
> > > Dropping the st_mult() does nothing to fix the actual problem (which is
> > > that this function should use a more appropriate type), but introduces
> > > new failure modes.
> >
> > Yes you're entirely right. I had some stupid blinders on while writing
> > this. FWIW I think I was experimenting with some local macros and
> > conflated a testing of the overflow of n*n in gdb with the caste'd
> > version, which you rightly point out here won't have the overflow issue
> > at all. Sorry.
>
> I'm not sure if this is helpful or not, but this is the minimal fix I
> came up with that runs the testcase I showed earlier. It's basically
> just swapping out "int" for "ssize_t" for any variables we use to index
> the arrays (though note a few are themselves held in arrays, and we have
> to cross some function boundaries).
>
> I won't be surprised if it doesn't hit all cases, or if it even hits a
> few it doesn't need to (e.g., should "phase" be dragged along with "i"
> and "j" in the first hunk?). I mostly did guess-and-check on the
> test-case, fixing whatever segfaulted and then running again until it
> worked. I didn't even really read the code very carefully.
>
> I think you _did_ do more of that careful reading, and broke down the
> refactorings into separate patches in your series. Which is good. So I
> think what we'd want is to pick out those parts of your series that end
> up switching the variable type. My goal in sharing this here is just to
> show that the end result of the fix can (and IMHO should) be around this
> same order of magnitude.

I am in favor of this patch. Will you have time to submit this with a
commit message?

Thank you,
Dscho

>
> ---
> diff --git a/linear-assignment.c b/linear-assignment.c
> index ecffc09be6..3efa30c50b 100644
> --- a/linear-assignment.c
> +++ b/linear-assignment.c
> @@ -13,11 +13,11 @@
>   * i is `cost[j + column_count * i].
>   */
>  void compute_assignment(int column_count, int row_count, int *cost,
> -			int *column2row, int *row2column)
> +			ssize_t *column2row, ssize_t *row2column)
>  {
>  	int *v, *d;
>  	int *free_row, free_count = 0, saved_free_count, *pred, *col;
> -	int i, j, phase;
> +	ssize_t i, j, phase;
>
>  	if (column_count < 2) {
>  		memset(column2row, 0, sizeof(int) * column_count);
> @@ -31,7 +31,7 @@ void compute_assignment(int column_count, int row_count, int *cost,
>
>  	/* column reduction */
>  	for (j = column_count - 1; j >= 0; j--) {
> -		int i1 = 0;
> +		ssize_t i1 = 0;
>
>  		for (i = 1; i < row_count; i++)
>  			if (COST(j, i1) > COST(j, i))
> @@ -51,7 +51,7 @@ void compute_assignment(int column_count, int row_count, int *cost,
>  	/* reduction transfer */
>  	ALLOC_ARRAY(free_row, row_count);
>  	for (i = 0; i < row_count; i++) {
> -		int j1 = row2column[i];
> +		ssize_t j1 = row2column[i];
>  		if (j1 == -1)
>  			free_row[free_count++] = i;
>  		else if (j1 < -1)
> @@ -74,13 +74,13 @@ void compute_assignment(int column_count, int row_count, int *cost,
>
>  	/* augmenting row reduction */
>  	for (phase = 0; phase < 2; phase++) {
> -		int k = 0;
> +		ssize_t k = 0;
>
>  		saved_free_count = free_count;
>  		free_count = 0;
>  		while (k < saved_free_count) {
>  			int u1, u2;
> -			int j1 = 0, j2, i0;
> +			ssize_t j1 = 0, j2, i0;
>
>  			i = free_row[k++];
>  			u1 = COST(j1, i) - v[j1];
> @@ -130,7 +130,7 @@ void compute_assignment(int column_count, int row_count, int *cost,
>  	ALLOC_ARRAY(pred, column_count);
>  	ALLOC_ARRAY(col, column_count);
>  	for (free_count = 0; free_count < saved_free_count; free_count++) {
> -		int i1 = free_row[free_count], low = 0, up = 0, last, k;
> +		ssize_t i1 = free_row[free_count], low = 0, up = 0, last, k;
>  		int min, c, u1;
>
>  		for (j = 0; j < column_count; j++) {
> @@ -192,7 +192,7 @@ void compute_assignment(int column_count, int row_count, int *cost,
>  		/* augmentation */
>  		do {
>  			if (j < 0)
> -				BUG("negative j: %d", j);
> +				BUG("negative j: %"PRIdMAX, (intmax_t)j);
>  			i = pred[j];
>  			column2row[j] = i;
>  			SWAP(j, row2column[i]);
> diff --git a/linear-assignment.h b/linear-assignment.h
> index 1dfea76629..7005521d61 100644
> --- a/linear-assignment.h
> +++ b/linear-assignment.h
> @@ -14,7 +14,7 @@
>   * row_count).
>   */
>  void compute_assignment(int column_count, int row_count, int *cost,
> -			int *column2row, int *row2column);
> +			ssize_t *column2row, ssize_t *row2column);
>
>  /* The maximal cost in the cost matrix (to prevent integer overflows). */
>  #define COST_MAX (1<<16)
> diff --git a/range-diff.c b/range-diff.c
> index cac89a2f4f..f1e1e27bf9 100644
> --- a/range-diff.c
> +++ b/range-diff.c
> @@ -308,9 +308,10 @@ static int diffsize(const char *a, const char *b)
>  static void get_correspondences(struct string_list *a, struct string_list *b,
>  				int creation_factor)
>  {
> -	int n = a->nr + b->nr;
> -	int *cost, c, *a2b, *b2a;
> -	int i, j;
> +	size_t n = a->nr + b->nr;
> +	int *cost, c;
> +	ssize_t *a2b, *b2a;
> +	size_t i, j;
>
>  	ALLOC_ARRAY(cost, st_mult(n, n));
>  	ALLOC_ARRAY(a2b, n);
>