Repository navigation
Integer dtype scalars truncate // and % for negative operands and panic on zero or MIN // -1 #1364
Description
The integer dtype scalars (pc.i8 … pc.i64, pc.u8 … pc.u64) implement // and % with Rust's truncating / and %. For negative operands they silently return results that differ from Python and NumPy. Division by zero and the signed MIN // -1 overflow panic, which surfaces as PanicException.
Reproduction
| Expression | pecos_rslib.dtypes |
NumPy 2 |
|---|---|---|
i64(-7) // 2 |
-3 |
-4 |
i64(-7) % 2 |
-1 |
1 |
7 // i64(-2) |
-3 |
-4 |
i32(7) % -2 |
1 |
-1 |
i64(1) // 0 |
PanicException: attempt to divide by zero |
0 (RuntimeWarning) |
u8(1) % 0 |
PanicException: attempt to calculate the remainder with a divisor of zero |
0 (RuntimeWarning) |
i64(-2**63) // -1 |
PanicException: attempt to divide with overflow |
-9223372036854775808 |
i8(-128) % -1 |
PanicException: attempt to calculate the remainder with overflow |
0 |
Cause
python/pecos-rslib/src/dtypes.rs: every integer scalar's __floordiv__, __rfloordiv__, __mod__ and __rmod__ compute self.value / other_value or self.value % other_value (for example ScalarI64::__floordiv__, ~3902 on dev; ScalarU8::__mod__, ~1077). Rust / truncates toward zero and % takes the sign of the dividend, while Python and NumPy floor and take the sign of the divisor. The unchecked operators also panic on a zero divisor and on MIN / -1. The same file already uses wrapping_add/wrapping_sub for +/-, so it intends NumPy-style wrapping integer semantics.
Direction
Implement floor division and modulo with Python/NumPy semantics for every signed type (div_euclid is not the same: it differs from floor division for negative divisors), wrapping MIN // -1 like NumPy. Decide deliberately on division by zero: NumPy returns 0 with a RuntimeWarning, Python ints raise ZeroDivisionError. Either is fine, but never a panic. Add tests against NumPy for every integer type, both operand orders, and the zero and overflow cases.
Found while preparing #1342 (float dtype scalar arithmetic).
Activity