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libkern: avoid local var in order_base_2()

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order_base_2(n) is implemented with a variable, which keeps it from
being used at file scope. Implement it instead as ilog2(2*n-1), which
produces a different result when 2*n overflows, which appears unlikely
in practice.

Reviewed by:	bz
Differential Revision:	https://reviews.freebsd.org/D46826
This commit is contained in:
Doug Moore 2024-09-27 18:43:07 -05:00
parent 86fc6f838e
commit b7cbf741d5
1 changed files with 1 additions and 4 deletions
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5
sys/sys/libkern.h
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@ -227,10 +227,7 @@ ilog2_long_long(long long n)
#define ilog2(n) (__builtin_constant_p(n) ? ilog2_const(n) : ilog2_var(n))
#define rounddown_pow_of_two(n) ((__typeof(n))1 << ilog2(n))
#define order_base_2(n) ({ \
__typeof(n) _n = (n); \
_n == 1 ? 0 : 1 + ilog2(_n - 1); \
})
#define order_base_2(n) ilog2(2*(n)-1)
#define roundup_pow_of_two(n) ((__typeof(n))1 << order_base_2(n))
#define bitcount64(x) __bitcount64((uint64_t)(x))