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xo-arena: DArenaHashMap: improve sentinel abstraction for control

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This commit is contained in:
Roland Conybeare 2026-01-08 12:41:29 -05:00
commit dcd8ced1cd
2 changed files with 27 additions and 69 deletions
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44
include/xo/arena/DArenaHashMap.hpp
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@ -64,6 +64,8 @@ namespace xo {
using size_type = std::size_t;
using control_type = std::uint8_t;
/** control: mask for sentinel states **/
static constexpr uint8_t c_sentinel_mask = 0xF0;
/** control: sentinel for empty slot **/
static constexpr uint8_t c_empty_slot = 0xFF;
/** control: tombstone for deleted slot **/
@ -75,6 +77,16 @@ namespace xo {
/** max load factor **/
static constexpr float c_max_load_factor = 0.875;
/** control: true for sentinel values **/
static constexpr bool is_sentinel(control_type ctrl) {
return ctrl & c_sentinel_mask;
}
/** control; true for non-sentinel values **/
static constexpr bool is_data(control_type ctrl) {
return 0 == (ctrl & c_sentinel_mask);
}
/** find smallest multiple k : k * c_group_size >= n **/
static size_type lub_group_mult(size_t n) {
return (n + c_group_size - 1) / c_group_size;
@ -288,7 +300,7 @@ namespace xo {
}
bool is_sentinel() const {
return ((*ctrl_ == c_tombstone) || (*ctrl_ == c_empty_slot));
return DArenaHashMapUtil::is_sentinel(*ctrl_);
}
private:
@ -605,20 +617,18 @@ namespace xo {
uint8_t ctrl = store_.control_[i];
value_type & kv_pair = store_.slots_[i];
if ((ctrl != c_empty_slot)
&& (ctrl != c_tombstone))
{
size_type h = hash_(kv_pair.first);
auto chk = this->_try_insert_aux(h, kv_pair, &store_2x);
if (DArenaHashMapUtil::is_data(ctrl)) {
size_type h = hash_(kv_pair.first);
auto chk = this->_try_insert_aux(h, kv_pair, &store_2x);
if (!chk.second) {
// shenanigans - something isn't right.
// - may have run out of memory
assert(false);
if (!chk.second) {
// shenanigans - something isn't right.
// - may have run out of memory
assert(false);
return false;
}
return false;
}
}
}
this->store_ = std::move(store_2x);
@ -778,7 +788,7 @@ namespace xo {
size_type occupied_count = 0;
for (size_type i = 0; i < store_.n_slot_; ++i) {
uint8_t c = store_.control_[i];
if ((c != c_empty_slot) && (c != c_tombstone)) {
if (DArenaHashMapUtil::is_data(c)) {
++occupied_count;
}
}
@ -793,7 +803,7 @@ namespace xo {
/* SM4.1.1: if control_[i] is non-sentinel, control_[i] = hash_(slots_[i].first) & 0x7f */
for (size_type i = 0; i < store_.n_slot_; ++i) {
uint8_t c = store_.control_[i];
if ((c != c_empty_slot) && (c != c_tombstone)) {
if (DArenaHashMapUtil::is_data(c)) {
uint8_t expected_h2 = hash_(store_.slots_[i].first) & 0x7f;
if (c != expected_h2) {
return policy.report_error(log,
@ -810,12 +820,12 @@ namespace xo {
*/
for (size_type i = 0; i < store_.n_slot_; ++i) {
uint8_t c = store_.control_[i];
if ((c != c_empty_slot) && (c != c_tombstone)) {
if (DArenaHashMapUtil::is_data(c)) {
size_type h = (hash_(store_.slots_[i].first) >> 7) & (store_.n_slot_ - 1);
size_type j = h;
while (j != i) {
uint8_t cj = store_.control_[j];
if ((cj == c_empty_slot) || (cj == c_tombstone)) {
if (DArenaHashMapUtil::is_sentinel(cj)) {
return policy.report_error(log,
c_self, ": expect non-empty slot in probe range [h..i]",
xtag("i", i),
@ -831,7 +841,7 @@ namespace xo {
/* SM4.2: if control_[i] is empty or tombstone, slots_[i].first = key_type() */
for (size_type i = 0; i < store_.n_slot_; ++i) {
uint8_t c = store_.control_[i];
if ((c == c_empty_slot) || (c == c_tombstone)) {
if (DArenaHashMapUtil::is_sentinel(c)) {
if (!(store_.slots_[i].first == key_type())) {
return policy.report_error(log,
c_self, ": expect empty/tombstone slot has default key",