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>

diff --git a/shallow.c b/shallow.c
index 4c4486ad67e05923b9826e9a3c7e091a826a4f83..2bf25552f045dffa62b3e6ca9f7d52106f6cd23b 100644 (file)
--- a/shallow.c
+++ b/shallow.c
@@ -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]++;
 }