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Correct calculation of vector element size (#5831)

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Number of elements on the stack shouldn't affect the calculation
of ElemWidth(). Variable 'start' needs to be subtracted from the
loop variable 'i' to make indexing zero-based.

There is an additional unit test to pack nested vectors. Size of
the packed buffer *without* this fix is 798 and only 664 bytes
*with* the fix.
This commit is contained in:
Dmitriy Kovalev
2020-03-26 08:54:52 -07:00
committed by GitHub
parent 6b271b7ecb
commit c37c989ed6
2 changed files with 13 additions and 1 deletions
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3
include/flatbuffers/flexbuffers.h
View File

@@ -1522,7 +1522,8 @@ class Builder FLATBUFFERS_FINAL_CLASS {
Type vector_type = FBT_KEY; Type vector_type = FBT_KEY;
// Check bit widths and types for all elements. // Check bit widths and types for all elements.
for (size_t i = start; i < stack_.size(); i += step) { for (size_t i = start; i < stack_.size(); i += step) {
auto elem_width = stack_[i].ElemWidth(buf_.size(), i + prefix_elems); auto elem_width =
stack_[i].ElemWidth(buf_.size(), i - start + prefix_elems);
bit_width = (std::max)(bit_width, elem_width); bit_width = (std::max)(bit_width, elem_width);
if (typed) { if (typed) {
if (i == start) { if (i == start) {

11
tests/test.cpp
View File

@@ -2885,6 +2885,17 @@ void FlexBuffersTest() {
// And from FlexBuffer back to JSON: // And from FlexBuffer back to JSON:
auto jsonback = jroot.ToString(); auto jsonback = jroot.ToString();
TEST_EQ_STR(jsontest, jsonback.c_str()); TEST_EQ_STR(jsontest, jsonback.c_str());
slb.Clear();
slb.Vector([&]() {
for (int i = 0; i < 130; ++i) slb.Add(static_cast<uint8_t>(255));
slb.Vector([&]() {
for (int i = 0; i < 130; ++i) slb.Add(static_cast<uint8_t>(255));
slb.Vector([] {});
});
});
slb.Finish();
TEST_EQ(slb.GetSize(), 664);
} }
void FlexBuffersDeprecatedTest() { void FlexBuffersDeprecatedTest() {