@matheusbsbs / matheus-bagliano / commits / 1127b3ced5

shallow.c: bit manipulation tweaks

First of all, 1 << 31 is technically undefined behaviour, so let's just use an unsigned literal. If i is 'signed int' and gcc doesn't know that i is positive, gcc generates code to compute the C99-mandated values of "i / 32" and "i % 32", which is a lot more complicated than simple a simple shifts/mask. The only caller of paint_down actually passes an "unsigned int" value, but the prototype of paint_down causes (completely well-defined) conversion to signed int, and gcc has no way of knowing that the converted value is non-negative. Just make the id parameter unsigned. In update_refstatus, the change in generated code is much smaller, presumably because gcc is smart enough to see that i starts as 0 and is only incremented, so it is allowed (per the UD of signed overflow) to assume that i is always non-negative. But let's just help less smart compilers generate good code anyway. Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Reviewed-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Rasmus Villemoes committed Dec 6, 2016 at 19:53 UTC 1127b3ced55b97229c55ff0c7585b284e3551a9e

1 file changed +4 -4

shallow.c

+4 -4

@@ -389,7 +389,7 @@ static uint32_t *paint_alloc(struct paint_info *info)

389 * all walked commits.

390 */

391 static void paint_down(struct paint_info *info, const unsigned char *sha1,

392 - int id)

392 + unsigned int id)

393 {

394 unsigned int i, nr;

395 struct commit_list *head = NULL;

@@ -401,7 +401,7 @@ static void paint_down(struct paint_info *info, const unsigned char *sha1,

401 if (!c)

402 return;

403 memset(bitmap, 0, bitmap_size);

404 - bitmap[id / 32] |= (1 << (id % 32));

404 + bitmap[id / 32] |= (1U << (id % 32));

405 commit_list_insert(c, &head);

406 while (head) {

407 struct commit_list *p;

@@ -575,11 +575,11 @@ static int add_ref(const char *refname, const struct object_id *oid,

575

576 static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)

577 {

578 - int i;

578 + unsigned int i;

579 if (!ref_status)

580 return;

581 for (i = 0; i < nr; i++)

582 - if (bitmap[i / 32] & (1 << (i % 32)))

582 + if (bitmap[i / 32] & (1U << (i % 32)))

583 ref_status[i]++;

584 }

585