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py/objint_longlong: Fix left shift of negative values.

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Previous comment was wrong, left shifting a negative value is UB in C. Use
the same approach as small int shifts (from runtime.c).

Signed-off-by: Angus Gratton <angus@redyak.com.au>
This commit is contained in:
Angus Gratton
2025-07-22 10:48:16 +10:00
committed by Damien George
parent 3185bb5827
commit 5d9ef6bfb6
1 changed files with 5 additions and 5 deletions
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10
py/objint_longlong.c
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@@ -208,14 +208,14 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
case MP_BINARY_OP_LSHIFT: case MP_BINARY_OP_LSHIFT:
case MP_BINARY_OP_INPLACE_LSHIFT: case MP_BINARY_OP_INPLACE_LSHIFT:
if ((int)rhs_val < 0) { if (rhs_val < 0) {
// negative shift not allowed // negative shift not allowed
mp_raise_ValueError(MP_ERROR_TEXT("negative shift count")); mp_raise_ValueError(MP_ERROR_TEXT("negative shift count"));
} }
result = lhs_val << (int)rhs_val; overflow = rhs_val >= (sizeof(long long) * MP_BITS_PER_BYTE)
// Left-shifting of negative values is implementation defined in C, but assume compiler || lhs_val > (LLONG_MAX >> rhs_val)
// will give us typical 2s complement behaviour unless the value overflows || lhs_val < (LLONG_MIN >> rhs_val);
overflow = rhs_val > 0 && ((lhs_val >= 0 && result < lhs_val) || (lhs_val < 0 && result > lhs_val)); result = (unsigned long long)lhs_val << rhs_val;
break; break;
case MP_BINARY_OP_RSHIFT: case MP_BINARY_OP_RSHIFT:
case MP_BINARY_OP_INPLACE_RSHIFT: case MP_BINARY_OP_INPLACE_RSHIFT: