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util: MAX_FROM_BITS() should be unsigned

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MAX_FROM_BITS() computes the maximum value representable in a number of
bits.  The expression for that is an unsigned value, but we explicitly cast
it to a signed int.  It looks like this is because one of the main users is
for FD_REF_MAX, which is used to bound fd values, typically stored as a
signed int.

The value MAX_FROM_BITS() is calculating is naturally non-negative, though,
so it makes more sense for it to be unsigned, and to move the case to the
definition of FD_REF_MAX.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-11-30 13:02:11 +11:00 committed by Stefano Brivio
parent e2e8219f13
commit 9d44aba7e0
2 changed files with 2 additions and 2 deletions
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2
passt.h
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@ -87,7 +87,7 @@ union epoll_ref {
struct {
enum epoll_type type:8;
#define FD_REF_BITS 24
#define FD_REF_MAX MAX_FROM_BITS(FD_REF_BITS)
#define FD_REF_MAX ((int)MAX_FROM_BITS(FD_REF_BITS))
int32_t fd:FD_REF_BITS;
union {
union tcp_epoll_ref tcp;

2
util.h
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@ -43,7 +43,7 @@
#define ROUND_DOWN(x, y) ((x) & ~((y) - 1))
#define ROUND_UP(x, y) (((x) + (y) - 1) & ~((y) - 1))
#define MAX_FROM_BITS(n) ((int)((1U << (n)) - 1))
#define MAX_FROM_BITS(n) (((1U << (n)) - 1))
#define BIT(n) (1UL << (n))
#define BITMAP_BIT(n) (BIT((n) % (sizeof(long) * 8)))