enhance: Add util::likely_size_on_disk

2 files changed, 22 insertions, 2 deletions

diff --git a/src/util/file.hpp b/src/util/file.hpp
index bb0c8b22..c74b58dc 100644
--- a/src/util/file.hpp
+++ b/src/util/file.hpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2021-2022 Joel Rosdahl and other contributors
+// Copyright (C) 2021-2023 Joel Rosdahl and other contributors
 //
 // See doc/AUTHORS.adoc for a complete list of contributors.
 //
@@ -39,6 +39,9 @@ enum class InPlace { yes, no };
 
 void create_cachedir_tag(const std::string& dir);
 
+// Return how much a file of `size` bytes likely would take on disk.
+uint64_t likely_size_on_disk(uint64_t size);
+
 // Read data from `fd` until end of file and call `data_receiver` with the read
 // data. Returns an error if the underlying read(2) call returned -1.
 nonstd::expected<void, std::string> read_fd(int fd, DataReceiver data_receiver);
@@ -87,4 +90,12 @@ nonstd::expected<void, std::string> write_file(const std::string& path,
                                                nonstd::span<const uint8_t> data,
                                                InPlace in_place = InPlace::no);
 
+// --- Inline implementations ---
+
+inline uint64_t
+likely_size_on_disk(uint64_t size)
+{
+  return (size + 4095) & ~4095;
+}
+
 } // namespace util
diff --git a/unittest/test_util_file.cpp b/unittest/test_util_file.cpp
index b1222b43..3cf09281 100644
--- a/unittest/test_util_file.cpp
+++ b/unittest/test_util_file.cpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2022 Joel Rosdahl and other contributors
+// Copyright (C) 2022-2023 Joel Rosdahl and other contributors
 //
 // See doc/AUTHORS.adoc for a complete list of contributors.
 //
@@ -29,6 +29,15 @@
 
 using TestUtil::TestContext;
 
+TEST_CASE("util::likely_size_on_disk")
+{
+  CHECK(util::likely_size_on_disk(0) == 0);
+  CHECK(util::likely_size_on_disk(1) == 4096);
+  CHECK(util::likely_size_on_disk(4095) == 4096);
+  CHECK(util::likely_size_on_disk(4096) == 4096);
+  CHECK(util::likely_size_on_disk(4097) == 8192);
+}
+
 TEST_CASE("util::read_file and util::write_file, text data")
 {
   TestContext test_context;