fix(chainbase): Implicit narrowing conversion in compound assignment

[ptrgits]

Compound assignment statements of the form x += y or x *= y perform an implicit narrowing conversion if the type of x is narrower than the type of y. For example, x += y is equivalent to x = (T)(x + y), where T is the type of x. This can result in information loss and numeric errors such as overflows.

---

fix the problem, we should avoid the implicit narrowing conversion in the compound assignment. Instead of using v += 27; (which implicitly casts the result of v + 27 from int to byte), we should perform the addition in int and then explicitly cast the result to byte when assigning it back to v. This makes the narrowing conversion explicit and clear to readers and static analysis tools.

Specifically, in getBase64FromByteString, replace:

if (v < 27) {
  v += 27; //revId -> v
}

with:

if (v < 27) {
  v = (byte)(v + 27); //revId -> v
}

No new imports or method definitions are needed.

References

Compound Assignment Operators, Narrowing Primitive Conversion
SEI CERT Oracle Coding Standard for Java: NUM00-J. Detect or prevent integer overflow

[troncommons]

Hi, thank you very much for your work!
This optimization has been merged to release_v4.8.1 branch through this PR #6417, and will be included in the upcoming v4.8.1 release.