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shallow.c: bit manipulation tweaks

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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>
This commit is contained in:
Rasmus Villemoes 2016-12-06 19:53:38 +07:00 committed by Junio C Hamano
parent 381aa8e730
commit 1127b3ced5
1 changed files with 4 additions and 4 deletions
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shallow.c
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@ -389,7 +389,7 @@ static uint32_t *paint_alloc(struct paint_info *info)
* all walked commits.
*/
static void paint_down(struct paint_info *info, const unsigned char *sha1,
int id)
unsigned int id)
{
unsigned int i, nr;
struct commit_list *head = NULL;
@ -401,7 +401,7 @@ static void paint_down(struct paint_info *info, const unsigned char *sha1,
if (!c)
return;
memset(bitmap, 0, bitmap_size);
bitmap[id / 32] |= (1 << (id % 32));
bitmap[id / 32] |= (1U << (id % 32));
commit_list_insert(c, &head);
while (head) {
struct commit_list *p;
@ -575,11 +575,11 @@ static int add_ref(const char *refname, const struct object_id *oid,
static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)
{
int i;
unsigned int i;
if (!ref_status)
return;
for (i = 0; i < nr; i++)
if (bitmap[i / 32] & (1 << (i % 32)))
if (bitmap[i / 32] & (1U << (i % 32)))
ref_status[i]++;
}