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Simplify choice and majority functions in digest helpers - #2559
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Reduce the bitwise operation count in twelve existing helpers across MD4, MD5, SHA-1, RIPEMD160, RIPEMD320 and SM3. Keep callers unchanged. The substitutions preserve int behavior and add no branches or locals. Generated and independently checked by the Sandbox mathematics cleanup: https://github.com/carstenartur/sandbox Sandbox source: d426c5cb6098f4377e45bc912469f160c38459ad AI-assisted extraction, review and validation.
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🟢 Approval recommended
No active review issues are reported for the digest-expression simplifications.
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What changed in this PR
This PR simplifies twelve choice and majority expressions in six core digest implementations, preserving Java int behavior while reducing each expression by one bitwise operation.
Changes:
- Rewrites nine choice expressions using XOR-based identities.
- Factors three majority expressions to reduce repeated operations.
- Leaves callers, interfaces, and control flow unchanged; no runtime performance improvement is claimed.
| File | Description |
|---|---|
core/src/main/java/org/bouncycastle/crypto/digests/SM3Digest.java |
Simplifies majority FF1 and choice GG1. |
core/src/main/java/org/bouncycastle/crypto/digests/SHA1Digest.java |
Simplifies choice f and majority g. |
core/src/main/java/org/bouncycastle/crypto/digests/RIPEMD320Digest.java |
Simplifies choice functions f2 and f4. |
core/src/main/java/org/bouncycastle/crypto/digests/RIPEMD160Digest.java |
Simplifies choice functions f2 and f4. |
core/src/main/java/org/bouncycastle/crypto/digests/MD5Digest.java |
Simplifies choice functions F and G. |
core/src/main/java/org/bouncycastle/crypto/digests/MD4Digest.java |
Simplifies choice F and majority G. |
Review effort: Balanced
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Simplify twelve existing choice/majority helper return expressions in MD4, MD5, SHA-1, RIPEMD160, RIPEMD320 and SM3.
Nine choice expressions use three bitwise operations instead of four; three majority expressions use four instead of five. The identities preserve Java int behavior and add no calls, branches, guards or local variables. Callers remain unchanged. Already simplified SHA-2/LongDigest helpers are excluded.
Generated and independently checked by the Sandbox mathematics cleanup:
https://github.com/carstenartur/sandbox
Sandbox revision: d426c5cb6098f4377e45bc912469f160c38459ad.
Every selected edit has PRESERVE_JAVA, BITVECTOR_TRUTH_TABLE and guard NONE evidence, and occurs in the actual complete generated sources. The same edits were reproduced in both completed full-corpus scans.
Validation on upstream e40316b:
No full Gradle build or runtime benchmark is claimed. ChatGPT assisted with extraction, review and validation.