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#include "upbc/message_layout.h"
#include "google/protobuf/descriptor.pb.h"
namespace upbc {
namespace protobuf = ::google::protobuf;
static int64_t DivRoundUp(int64_t a, int64_t b) {
ABSL_ASSERT(a >= 0);
ABSL_ASSERT(b > 0);
return (a + b - 1) / b;
}
MessageLayout::Size MessageLayout::Place(
MessageLayout::SizeAndAlign size_and_align) {
Size offset = size_;
offset.AlignUp(size_and_align.align);
size_ = offset;
size_.Add(size_and_align.size);
//maxalign_.MaxFrom(size_and_align.align);
maxalign_.MaxFrom(size_and_align.size);
return offset;
}
bool MessageLayout::HasHasbit(const protobuf::FieldDescriptor* field) {
return field->file()->syntax() == protobuf::FileDescriptor::SYNTAX_PROTO2 &&
field->label() != protobuf::FieldDescriptor::LABEL_REPEATED &&
!field->containing_oneof() &&
!field->containing_type()->options().map_entry();
}
MessageLayout::SizeAndAlign MessageLayout::SizeOf(
const protobuf::FieldDescriptor* field) {
if (field->is_repeated()) {
return {{4, 8}, {4, 8}}; // Pointer to array object.
} else {
return SizeOfUnwrapped(field);
}
}
MessageLayout::SizeAndAlign MessageLayout::SizeOfUnwrapped(
const protobuf::FieldDescriptor* field) {
switch (field->cpp_type()) {
case protobuf::FieldDescriptor::CPPTYPE_MESSAGE:
return {{4, 8}, {4, 8}}; // Pointer to message.
case protobuf::FieldDescriptor::CPPTYPE_STRING:
return {{8, 16}, {4, 8}}; // upb_strview
case protobuf::FieldDescriptor::CPPTYPE_BOOL:
return {{1, 1}, {1, 1}};
case protobuf::FieldDescriptor::CPPTYPE_FLOAT:
case protobuf::FieldDescriptor::CPPTYPE_INT32:
case protobuf::FieldDescriptor::CPPTYPE_UINT32:
return {{4, 4}, {4, 4}};
default:
return {{8, 8}, {8, 8}};
}
}
int64_t MessageLayout::FieldLayoutRank(const protobuf::FieldDescriptor* field) {
// Order:
// 1, 2, 3. primitive fields (8, 4, 1 byte)
// 4. string fields
// 5. submessage fields
// 6. repeated fields
//
// This has the following nice properties:
//
// 1. padding alignment is (nearly) minimized.
// 2. fields that might have defaults (1-4) are segregated
// from fields that are always zero-initialized (5-7).
//
// We skip oneof fields, because they are emitted in a separate pass.
int64_t rank;
if (field->containing_oneof()) {
fprintf(stderr, "shouldn't have oneofs here.\n");
abort();
} else if (field->label() == protobuf::FieldDescriptor::LABEL_REPEATED) {
rank = 6;
} else {
switch (field->cpp_type()) {
case protobuf::FieldDescriptor::CPPTYPE_MESSAGE:
rank = 5;
break;
case protobuf::FieldDescriptor::CPPTYPE_STRING:
rank = 4;
break;
case protobuf::FieldDescriptor::CPPTYPE_BOOL:
rank = 3;
break;
case protobuf::FieldDescriptor::CPPTYPE_FLOAT:
case protobuf::FieldDescriptor::CPPTYPE_INT32:
case protobuf::FieldDescriptor::CPPTYPE_UINT32:
rank = 2;
break;
default:
rank = 1;
break;
}
}
// Break ties with field number.
return (rank << 29) | field->number();
}
void MessageLayout::ComputeLayout(const protobuf::Descriptor* descriptor) {
size_ = Size{0, 0};
maxalign_ = Size{0, 0};
if (descriptor->options().map_entry()) {
// Map entries aren't actually stored, they are only used during parsing.
// For parsing, it helps a lot if all map entry messages have the same
// layout.
SizeAndAlign size{{8, 16}, {4, 8}}; // upb_strview
field_offsets_[descriptor->FindFieldByNumber(1)] = Place(size);
field_offsets_[descriptor->FindFieldByNumber(2)] = Place(size);
} else {
PlaceNonOneofFields(descriptor);
PlaceOneofFields(descriptor);
}
// Align overall size up to max size.
size_.AlignUp(maxalign_);
}
void MessageLayout::PlaceNonOneofFields(
const protobuf::Descriptor* descriptor) {
std::vector<const protobuf::FieldDescriptor*> field_order;
for (int i = 0; i < descriptor->field_count(); i++) {
const protobuf::FieldDescriptor* field = descriptor->field(i);
if (!field->containing_oneof()) {
field_order.push_back(descriptor->field(i));
}
}
std::sort(field_order.begin(), field_order.end(),
[](const protobuf::FieldDescriptor* a,
const protobuf::FieldDescriptor* b) {
return FieldLayoutRank(a) < FieldLayoutRank(b);
});
// Place/count hasbits.
int hasbit_count = 0;
for (auto field : field_order) {
if (HasHasbit(field)) {
// We don't use hasbit 0, so that 0 can indicate "no presence" in the
// table. This wastes one hasbit, but we don't worry about it for now.
hasbit_indexes_[field] = ++hasbit_count;
}
}
// Place hasbits at the beginning.
int64_t hasbit_bytes = DivRoundUp(hasbit_count, 8);
Place(SizeAndAlign{{hasbit_bytes, hasbit_bytes}, {1, 1}});
// Place non-oneof fields.
for (auto field : field_order) {
field_offsets_[field] = Place(SizeOf(field));
}
}
void MessageLayout::PlaceOneofFields(const protobuf::Descriptor* descriptor) {
std::vector<const protobuf::OneofDescriptor*> oneof_order;
for (int i = 0; i < descriptor->oneof_decl_count(); i++) {
oneof_order.push_back(descriptor->oneof_decl(i));
}
std::sort(oneof_order.begin(), oneof_order.end(),
[](const protobuf::OneofDescriptor* a,
const protobuf::OneofDescriptor* b) {
return a->full_name() < b->full_name();
});
for (auto oneof : oneof_order) {
SizeAndAlign oneof_maxsize{{0, 0}, {0, 0}};
// Calculate max size.
for (int i = 0; i < oneof->field_count(); i++) {
oneof_maxsize.MaxFrom(SizeOf(oneof->field(i)));
}
// Place discriminator enum and data.
Size data = Place(oneof_maxsize);
Size discriminator = Place(SizeAndAlign{{4, 4}, {4, 4}});
oneof_case_offsets_[oneof] = discriminator;
for (int i = 0; i < oneof->field_count(); i++) {
field_offsets_[oneof->field(i)] = data;
}
}
}
} // namespace upbc
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