Merge #17917: tests: Add amount compression/decompression fuzzing to existing fuzzing harness

7e9c7113afbed96cef80c327cc93e82000d6bb69 compressor: Make the domain of CompressAmount(...) explicit (practicalswift)
4a7fd7a7124f84e010b01d0769ef0572bf031ee8 tests: Add amount compression/decompression fuzzing to existing fuzzing harness: test compression round-trip (practicalswift)

Pull request description:

  Small fuzzing improvement:

  Add amount compression/decompression fuzzing to existing fuzzing harness: test compression round-trip (`DecompressAmount(CompressAmount(…))`).

  Make the domain of `CompressAmount(…)` explicit.

  Amount compression primer:

  ```
      Compact serialization for amounts

      Special serializer/deserializer for amount values. It is optimized for
      values which have few non-zero digits in decimal representation. Most
      amounts currently in the txout set take only 1 or 2 bytes to
      represent.
  ```

  **How to test this PR**

  ```
  $ make distclean
  $ ./autogen.sh
  $ CC=clang CXX=clang++ ./configure --enable-fuzz \
        --with-sanitizers=address,fuzzer,undefined
  $ make
  $ src/test/fuzz/integer
  …
  ```

Top commit has no ACKs.

Tree-SHA512: 0f7c05b97012ccd5cd05a96c209e6b4d7d2fa73138bac9615cf531baa3f614f9003e29a198015bcc083af9f5bdc752bb52615b82c5df3c519b1a064bd4fc6664

1 files changed, 10 insertions, 0 deletions

diff --git a/src/compressor.h b/src/compressor.h
index 7bb60d311e..223603e7e9 100644
--- a/src/compressor.h
+++ b/src/compressor.h
@@ -15,7 +15,17 @@ bool CompressScript(const CScript& script, std::vector<unsigned char> &out);
 unsigned int GetSpecialScriptSize(unsigned int nSize);
 bool DecompressScript(CScript& script, unsigned int nSize, const std::vector<unsigned char> &out);
 
+/**
+ * Compress amount.
+ *
+ * nAmount is of type uint64_t and thus cannot be negative. If you're passing in
+ * a CAmount (int64_t), make sure to properly handle the case where the amount
+ * is negative before calling CompressAmount(...).
+ *
+ * @pre Function defined only for 0 <= nAmount <= MAX_MONEY.
+ */
 uint64_t CompressAmount(uint64_t nAmount);
+
 uint64_t DecompressAmount(uint64_t nAmount);
 
 /** Compact serializer for scripts.