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lib: cgen: make _bf_round_next_power_of_2 correct #494

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Merged
pzmarzly merged 1 commit into from
Apr 1, 2026
+6 −0
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lib: cgen: make _bf_round_next_power_of_2 correct #494

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6 changes: 6 additions & 0 deletions src/libbpfilter/cgen/program.c
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Original file line number Diff line number Diff line change
Expand Up @@ -65,12 +65,18 @@

static inline size_t _bf_round_next_power_of_2(size_t value)
{
if (value == 0)
return 1;

value--;
value |= value >> 1;
value |= value >> 2;
value |= value >> 4;
value |= value >> 8;
value |= value >> 16;
#if SIZE_MAX > 0xFFFFFFFFU
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@github-actions github-actions bot Mar 31, 2026

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Claude: suggestion: Pre-existing: _bf_round_next_power_of_2(0) returns 0 due to unsigned wrap-around (0 - 1 wraps to SIZE_MAX, OR-shifts fill all bits, then ++value wraps back to 0). Since you're already touching this function, consider adding a guard:

static inline size_t _bf_round_next_power_of_2(size_t value)
{
    if (value == 0)
        return 1;

    value--;
    ...

Neither current call site can pass 0 (sizeof(struct bf_log) * _BF_LOG_MAP_N_ENTRIES is always positive), so this is not blocking — just a defensive improvement for future callers.

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@pzmarzly pzmarzly Mar 31, 2026

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That's true, and it is something I stumbled upon already when using this function for bf_hashset (where initial capacity was 0).

2**0 == 1, but here _bf_round_next_power_of_2(0) == 0.

I'll address this here in this PR as well, but I'll let reviewer decide if this should be merged together.

value |= value >> 32;
#endif

return ++value;
}
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