Rust `BIG`/`DBIG` `cmove` panics due to arithmetic overflow

[DJAndries]

The cmove method of BIG and DBIG panics with certain values.

attempt to multiply with overflow
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/panicking.rs:692:5
   1: core::panicking::panic_fmt
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:75:14
   2: core::panicking::panic_const::panic_const_mul_overflow
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:178:21
   3: brave_miracl::bn254::dbig::DBIG::cmove
             at /miracl-rs/src/bn254/dbig.rs:149:61
   4: brave_miracl::bn254::dbig::DBIG::ctdmod
             at /miracl-rs/src/bn254/dbig.rs:223:13
   5: brave_miracl::bn254::dbig::DBIG::dmod
             at /miracl-rs/src/bn254/dbig.rs:237:9
   6: brave_miracl::bn254::big::BIG::randomnum
             at /miracl-rs/src/bn254/big.rs:751:9

[mcarrickscott]

Good catch! I forget to use wrapping semantics for debug mode. Now fixed...

…

On Wed, Sep 3, 2025 at 1:39 AM Darnell Andries ***@***.***> wrote: *DJAndries* created an issue (miracl/core#76) <#76> The cmove method of BIG and DBIG panics with certain values. attempt to multiply with overflow stack backtrace: 0: rust_begin_unwind at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/panicking.rs:692:5 1: core::panicking::panic_fmt at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:75:14 2: core::panicking::panic_const::panic_const_mul_overflow at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:178:21 3: brave_miracl::bn254::dbig::DBIG::cmove at /miracl-rs/src/bn254/dbig.rs:149:61 4: brave_miracl::bn254::dbig::DBIG::ctdmod at /miracl-rs/src/bn254/dbig.rs:223:13 5: brave_miracl::bn254::dbig::DBIG::dmod at /miracl-rs/src/bn254/dbig.rs:237:9 6: brave_miracl::bn254::big::BIG::randomnum at /miracl-rs/src/bn254/big.rs:751:9 — Reply to this email directly, view it on GitHub <#76>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAU3ZDS5QSUCI4NIYNNIXKD3QY2DJAVCNFSM6AAAAACFO4Q5UWVHI2DSMVQWIX3LMV43ASLTON2WKOZTGM3TOOBZGA3TSOI> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[DJAndries]

Good catch! I forget to use wrapping semantics for debug mode.

Now fixed...
…

Oh! I lodged a PR to fix the issue yesterday, but it looks like you decided to add a fix yourself. I just rebased my PR; perhaps the use of the Wrapping struct could make these operations less tedious. Feel free to close or merge: #77

[mcarrickscott]

I think I prefer to leave it as is. There are some subtleties, for example (w+1) can never overflow as w will always be even. But thanks again. Mike

…

On Wed, Sep 3, 2025 at 11:11 PM Darnell Andries ***@***.***> wrote: *DJAndries* left a comment (miracl/core#76) <#76 (comment)> Good catch! I forget to use wrapping semantics for debug mode. Now fixed... … <#m_6617558176531985040_> Oh! I lodged a PR to fix the issue yesterday, but it looks like you decided to add a fix yourself. I just rebased my PR; perhaps the use of the Wrapping struct could make these operations less tedious. Feel free to close or merge: #77 <#77> — Reply to this email directly, view it on GitHub <#76 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAU3ZDQAR5CSNUWTTAYZSUT3Q5RP3AVCNFSM6AAAAACFO4Q5UWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTENJQHE3TIMRTGY> . You are receiving this because you commented.Message ID: ***@***.***>