fix: BigInt256 modulo must use mathematical mod, not remainder#857
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fix: BigInt256 modulo must use mathematical mod, not remainder#857mwaddip wants to merge 1 commit into
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ErgoScript's % operator on BigInt maps to Java's BigInteger.mod() which always returns a non-negative result. sigma-rust was using checked_rem (Rust remainder semantics) which can return negative values for negative dividends. This causes consensus failures on mainnet — e.g. block 670,557 contains a script that checks `byteArrayToBigInt(boxId.slice(0,15)) % 5 == 2`. The box ID bytes produce a negative BigInt. Java's mod(5) returns 2, but Rust's rem(5) returns -3, causing the script to evaluate to false. The JVM sigmastate-interpreter explicitly documents this in BigIntegerOps.scala: "Even though this method is called divisionRemainder, the semantics of ErgoTree language requires it to correspond to BigInteger.mod" Fix: if checked_rem returns a negative result, add the divisor to make it non-negative. Only affects BigInt256; primitive integer types correctly use remainder semantics matching the JVM. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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BigInt256::checked_rem uses Rust remainder (%) and returns negative values for negative dividends; ErgoScript's % on BigInt maps to java.math.BigInteger.mod(), which is always non-negative. Mainnet block 670,557: byteArrayToBigInt(boxId.slice(0,15)) % 5 returns JVM 2 vs sigma-rust -3.
Fix only affects BigInt256; primitive int types keep remainder semantics — JVM uses % for those too.