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fix: negation of MIN_VALUE wraps to match sigma-state #870

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fix: negation of MIN_VALUE wraps to match sigma-state #870

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45 changes: 29 additions & 16 deletions ergotree-interpreter/src/eval/negation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,19 +18,21 @@ impl Evaluable for Negation {
fn overflow_err<T: core::fmt::Display>(v: &T) -> EvalError {
EvalError::ArithmeticException(format!("Overflow on Negation of value {}", *v))
}
fn neg<'ctx, T: CheckedNeg + Into<Value<'ctx>> + core::fmt::Display>(
v: &T,
) -> Result<Value<'ctx>, EvalError> {
v.checked_neg()
.map(|v| v.into())
.ok_or_else(|| overflow_err(v))
}
match input_v {
Value::Byte(v) => neg(&v),
Value::Short(v) => neg(&v),
Value::Int(v) => neg(&v),
Value::Long(v) => neg(&v),
Value::BigInt(v) => neg(&v),
// Fixed-width signed ints negate with two's-complement wrap
// (`-MIN == MIN`), matching sigma-state's unchecked numeric
// `negate` (`ast/trees.scala` Negation.eval) — negating MIN is
// not an error on the JVM.
Value::Byte(v) => Ok(v.wrapping_neg().into()),
Value::Short(v) => Ok(v.wrapping_neg().into()),
Value::Int(v) => Ok(v.wrapping_neg().into()),
Value::Long(v) => Ok(v.wrapping_neg().into()),
// BigInt256 stays checked: sigma-state's 256-bit BigInt also
// overflows negating its MIN (`-(2^255)`), so both sides error.
Value::BigInt(v) => v
.checked_neg()
.map(|v| v.into())
.ok_or_else(|| overflow_err(&v)),
_ => Err(EvalError::UnexpectedValue(format!(
"Expected Negation input to be numeric value, got {:?}",
input_v
Expand Down Expand Up @@ -67,14 +69,25 @@ mod tests {
#[test]
fn eval() {
assert_eq!(run_eval(1i8), -1i8);
assert!(try_run_eval(i8::MIN).is_err());
assert_eq!(run_eval(1i16), -1i16);
assert!(try_run_eval(i16::MIN).is_err());
assert_eq!(run_eval(1i32), -1i32);
assert!(try_run_eval(i32::MIN).is_err());
assert_eq!(run_eval(1i64), -1i64);
assert!(try_run_eval(i64::MIN).is_err());
assert_eq!(run_eval(BigInt256::from(1i64)), BigInt256::from(-1i64));
}

// JVM parity (sigma-state 6.0.3, LanguageSpecificationV5): negating a
// fixed-width MIN_VALUE two's-complement-wraps to itself (`-MIN == MIN`)
// with no error — sigma-state's `Negation.eval` uses the unchecked
// numeric `negate`. Repros: santa `vectors/eval/v5/Numeric_Negation_
// equivalence.json` (`-128#0`, `-32768#9`, `-2147483648#18`,
// `-9223372036854775808#26`). `BigInt256` is the exception — its 256-bit
// MIN (`-(2^255)`) overflows on both sides, so it still errors.
#[test]
fn negation_of_min_value_wraps_to_self() {
assert_eq!(run_eval(i8::MIN), i8::MIN);
assert_eq!(run_eval(i16::MIN), i16::MIN);
assert_eq!(run_eval(i32::MIN), i32::MIN);
assert_eq!(run_eval(i64::MIN), i64::MIN);
assert!(try_run_eval(BigInt256::min_value()).is_err());
}
}
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