[zip] Save 1 malloc and memset for each added file in ZipWriter
+ add a benchmark for the function.
This change speeds up the function by about 3%: 910ns->880ns
Change-Id: I33c8c31de18d10eb38f109917ecbcbdda45b4034
diff --git a/libziparchive/zip_writer.cc b/libziparchive/zip_writer.cc
index 3c53209..198154b 100644
--- a/libziparchive/zip_writer.cc
+++ b/libziparchive/zip_writer.cc
@@ -247,13 +247,24 @@
ExtractTimeAndDate(time, &file_entry.last_mod_time, &file_entry.last_mod_date);
off_t offset = current_offset_ + sizeof(LocalFileHeader) + file_entry.path.size();
- std::vector<char> zero_padding;
+ // prepare a pre-zeroed memory page in case when we need to pad some aligned data.
+ static constexpr auto kPageSize = 4096;
+ static constexpr char kSmallZeroPadding[kPageSize] = {};
+ // use this buffer if our preallocated one is too small
+ std::vector<char> zero_padding_big;
+ const char* zero_padding = nullptr;
+
if (alignment != 0 && (offset & (alignment - 1))) {
// Pad the extra field so the data will be aligned.
uint16_t padding = static_cast<uint16_t>(alignment - (offset % alignment));
file_entry.padding_length = padding;
offset += padding;
- zero_padding.resize(padding, 0);
+ if (padding <= std::size(kSmallZeroPadding)) {
+ zero_padding = kSmallZeroPadding;
+ } else {
+ zero_padding_big.resize(padding, 0);
+ zero_padding = zero_padding_big.data();
+ }
}
LocalFileHeader header = {};
@@ -269,7 +280,7 @@
return HandleError(kIoError);
}
- if (file_entry.padding_length != 0 && fwrite(zero_padding.data(), 1, file_entry.padding_length,
+ if (file_entry.padding_length != 0 && fwrite(zero_padding, 1, file_entry.padding_length,
file_) != file_entry.padding_length) {
return HandleError(kIoError);
}