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py: Handle small int power overflow correctly.

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This commit is contained in:
Damien George 2014-04-04 00:16:32 +01:00
parent 4b34c76fd6
commit 5bf565e353
2 changed files with 22 additions and 3 deletions
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5
py/mpz.c
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@ -993,8 +993,11 @@ void mpz_pow_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs) {
if (mpz_is_odd(n)) {
mpz_mul_inpl(dest, dest, x);
}
mpz_mul_inpl(x, x, x);
n->len = mpn_shr(n->dig, n->dig, n->len, 1);
if (n->len == 0) {
break;
}
mpz_mul_inpl(x, x, x);
}
mpz_free(x);

20
py/runtime.c
View File

@ -367,18 +367,34 @@ mp_obj_t mp_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
nlr_jump(mp_obj_new_exception_msg(&mp_type_ValueError, "negative power with no float support"));
#endif
} else {
// TODO check for overflow
machine_int_t ans = 1;
while (rhs_val > 0) {
if (rhs_val & 1) {
machine_int_t old = ans;
ans *= lhs_val;
if (ans < old) {
goto power_overflow;
}
}
if (rhs_val == 1) {
break;
}
lhs_val *= lhs_val;
rhs_val /= 2;
machine_int_t old = lhs_val;
lhs_val *= lhs_val;
if (lhs_val < old) {
goto power_overflow;
}
}
lhs_val = ans;
}
break;
power_overflow:
// use higher precision
lhs = mp_obj_new_int_from_ll(MP_OBJ_SMALL_INT_VALUE(lhs));
goto generic_binary_op;
case MP_BINARY_OP_LESS: return MP_BOOL(lhs_val < rhs_val); break;
case MP_BINARY_OP_MORE: return MP_BOOL(lhs_val > rhs_val); break;
case MP_BINARY_OP_LESS_EQUAL: return MP_BOOL(lhs_val <= rhs_val); break;