StringData* StringData::Make(const APCString* shared) {
// No need to check if len > MaxSize, because if it were we'd never
// have made the StringData in the APCVariant without throwing.
assert(size_t(shared->getStringData()->size()) <= size_t(MaxSize));
auto const data = shared->getStringData();
auto const len = data->size();
if (UNLIKELY(len > SmallStringReserve)) {
return MakeAPCSlowPath(shared);
}
// small-string path: make a flat copy.
static_assert(SmallStringReserve + kCapOverhead <= CapCode::Threshold, "");
static_assert(SmallStringReserve + kCapOverhead == 64, "");
auto const sd = allocFlatSmallImpl(SmallStringReserve);
sd->m_lenAndHash = data->m_lenAndHash;
auto const psrc = data->data();
auto const pdst = reinterpret_cast<char*>(sd + 1);
auto const mcret = memcpy(pdst, psrc, len + 1); // also copy the tailing 0
auto const ret = reinterpret_cast<StringData*>(mcret) - 1;
// Recalculating ret from mcret avoids a spill.
assert(ret == sd);
assert(ret->m_len == len);
assert(ret->hasExactlyOneRef());
assert(ret->m_hash == data->m_hash);
assert(ret->isFlat());
assert(ret->checkSane());
return ret;
}
StringData* StringData::Make(const APCString* shared) {
// No need to check if len > MaxSize, because if it were we'd never
// have made the StringData in the APCVariant without throwing.
assert(size_t(shared->getStringData()->size()) <= size_t(MaxSize));
auto const data = shared->getStringData();
auto const len = data->size();
if (UNLIKELY(len > SmallStringReserve)) {
return MakeAPCSlowPath(shared);
}
// small-string path
auto const psrc = data->data();
auto const hash = data->m_hash & STRHASH_MASK;
assert(hash != 0);
static_assert(SmallStringReserve + sizeof(StringData) + 1 <
CapCode::Threshold, "");
auto const need = sizeof(StringData) + len + 1;
auto const cap = MemoryManager::smallSizeClass(need);
auto const sd = static_cast<StringData*>(MM().mallocSmallSize(cap));
auto const pdst = reinterpret_cast<char*>(sd + 1);
auto const cc = CapCode::ceil(cap - kCapOverhead);
assert(cc.code == cap - kCapOverhead);
sd->m_data = pdst;
sd->m_hdr.init(cc, HeaderKind::String, 1);
sd->m_lenAndHash = len | int64_t{hash} << 32;
// pdst[len] = 0;
auto const mcret = memcpy(pdst, psrc, len + 1);
auto const ret = reinterpret_cast<StringData*>(mcret) - 1;
// Recalculating ret from mcret avoids a spill.
// Note: this return value thing is doing a dead lea into %rsi in
// the caller for some reason.
assert(ret == sd);
assert(ret->m_len == len);
assert(ret->hasExactlyOneRef());
assert(ret->m_hash == hash);
assert(ret->isFlat());
assert(ret->checkSane());
return ret;
}
