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Use trailing-zero builtin with older libc++ #243

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Use trailing-zero builtin with older libc++ #243

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4 changes: 3 additions & 1 deletion Sources/OpenAttributeGraphCxx/Data/table.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,9 @@ ptr<page> table::alloc_page(zone *zone, uint32_t needed_size) OAG_NOEXCEPT {
page_map_type free_pages_map = _page_maps[map_index].flip();
while (free_pages_map.any()) {

int candidate_bit = std::countr_zero(static_cast<uint64_t>(free_pages_map.to_ullong()));
// The loop guarantees a nonzero map; the builtin works with
// libc++ versions that predate std::countr_zero.
int candidate_bit = __builtin_ctzll(free_pages_map.to_ullong());

// scan ahead to find enough consecutive free pages
bool found = false;
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