From: "Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
To: git@vger.kernel.org
Cc: rv@rasmusvillemoes.dk, "Jeff King" <peff@peff.net>,
"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
Subject: [PATCH v2 5/6] shallow.c: bit manipulation tweaks
Date: Tue, 6 Dec 2016 19:53:38 +0700 [thread overview]
Message-ID: <20161206125339.16803-6-pclouds@gmail.com> (raw)
In-Reply-To: <20161206125339.16803-1-pclouds@gmail.com>
From: Rasmus Villemoes <rv@rasmusvillemoes.dk>
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>
---
shallow.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/shallow.c b/shallow.c
index 719f699..beb967e 100644
--- a/shallow.c
+++ b/shallow.c
@@ -467,7 +467,7 @@ 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;
@@ -479,7 +479,7 @@ 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;
@@ -653,11 +653,11 @@ 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]++;
}
--
2.8.2.524.g6ff3d78
next prev parent reply other threads:[~2016-12-06 12:55 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-02 20:31 [PATCH 1/4] shallow.c: make paint_alloc slightly more robust Rasmus Villemoes
2016-12-02 20:31 ` [PATCH 2/4] shallow.c: avoid theoretical pointer wrap-around Rasmus Villemoes
2016-12-03 5:17 ` Jeff King
2016-12-02 20:31 ` [PATCH 3/4] shallow.c: bit manipulation tweaks Rasmus Villemoes
2016-12-03 5:21 ` Jeff King
2016-12-02 20:31 ` [PATCH 4/4] shallow.c: remove useless test Rasmus Villemoes
2016-12-03 5:24 ` Jeff King
2016-12-05 12:00 ` Duy Nguyen
2016-12-03 5:14 ` [PATCH 1/4] shallow.c: make paint_alloc slightly more robust Jeff King
2016-12-05 10:02 ` Duy Nguyen
2016-12-06 12:53 ` [PATCH v2 0/6] shallow.c improvements Nguyễn Thái Ngọc Duy
2016-12-06 12:53 ` [PATCH v2 1/6] shallow.c: rename fields in paint_info to better express their purposes Nguyễn Thái Ngọc Duy
2016-12-06 12:53 ` [PATCH v2 2/6] shallow.c: stop abusing COMMIT_SLAB_SIZE for paint_info's memory pools Nguyễn Thái Ngọc Duy
2016-12-06 12:53 ` [PATCH v2 3/6] shallow.c: make paint_alloc slightly more robust Nguyễn Thái Ngọc Duy
2016-12-06 12:53 ` [PATCH v2 4/6] shallow.c: avoid theoretical pointer wrap-around Nguyễn Thái Ngọc Duy
2016-12-06 12:53 ` Nguyễn Thái Ngọc Duy [this message]
2016-12-06 12:53 ` [PATCH v2 6/6] shallow.c: remove useless code Nguyễn Thái Ngọc Duy
2016-12-06 13:42 ` [PATCH v2 0/6] shallow.c improvements Jeff King
2016-12-06 13:47 ` Duy Nguyen
2016-12-07 23:42 ` Junio C Hamano
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