return (PyObject *) z;
}
+/* Compute two's complement of digit vector a[0:m], writing result to
+ z[0:m]. The digit vector a need not be normalized, but should not
+ be entirely zero. a and z may point to the same digit vector. */
+
+static void
+v_complement(digit *z, digit *a, Py_ssize_t m)
+{
+ Py_ssize_t i;
+ digit carry = 1;
+ for (i = 0; i < m; ++i) {
+ carry += a[i] ^ PyLong_MASK;
+ z[i] = carry & PyLong_MASK;
+ carry >>= PyLong_SHIFT;
+ }
+ assert(carry == 0);
+}
/* Bitwise and/xor/or operations */
int op, /* '&', '|', '^' */
PyLongObject *b)
{
- digit maska, maskb; /* 0 or PyLong_MASK */
- int negz;
+ int nega, negb, negz;
Py_ssize_t size_a, size_b, size_z, i;
PyLongObject *z;
- digit diga, digb;
- PyObject *v;
- if (Py_SIZE(a) < 0) {
- a = (PyLongObject *) long_invert(a);
- if (a == NULL)
+ /* Bitwise operations for negative numbers operate as though
+ on a two's complement representation. So convert arguments
+ from sign-magnitude to two's complement, and convert the
+ result back to sign-magnitude at the end. */
+
+ /* If a is negative, replace it by its two's complement. */
+ size_a = ABS(Py_SIZE(a));
+ nega = Py_SIZE(a) < 0;
+ if (nega) {
+ z = _PyLong_New(size_a);
+ if (z == NULL)
return NULL;
- maska = PyLong_MASK;
+ v_complement(z->ob_digit, a->ob_digit, size_a);
+ a = z;
}
- else {
+ else
+ /* Keep reference count consistent. */
Py_INCREF(a);
- maska = 0;
- }
- if (Py_SIZE(b) < 0) {
- b = (PyLongObject *) long_invert(b);
- if (b == NULL) {
+
+ /* Same for b. */
+ size_b = ABS(Py_SIZE(b));
+ negb = Py_SIZE(b) < 0;
+ if (negb) {
+ z = _PyLong_New(size_b);
+ if (z == NULL) {
Py_DECREF(a);
return NULL;
}
- maskb = PyLong_MASK;
+ v_complement(z->ob_digit, b->ob_digit, size_b);
+ b = z;
}
- else {
+ else
Py_INCREF(b);
- maskb = 0;
+
+ /* Swap a and b if necessary to ensure size_a >= size_b. */
+ if (size_a < size_b) {
+ z = a; a = b; b = z;
+ size_z = size_a; size_a = size_b; size_b = size_z;
+ negz = nega; nega = negb; negb = negz;
}
- negz = 0;
+ /* JRH: The original logic here was to allocate the result value (z)
+ as the longer of the two operands. However, there are some cases
+ where the result is guaranteed to be shorter than that: AND of two
+ positives, OR of two negatives: use the shorter number. AND with
+ mixed signs: use the positive number. OR with mixed signs: use the
+ negative number.
+ */
switch (op) {
case '^':
- if (maska != maskb) {
- maska ^= PyLong_MASK;
- negz = -1;
- }
+ negz = nega ^ negb;
+ size_z = size_a;
break;
case '&':
- if (maska && maskb) {
- op = '|';
- maska ^= PyLong_MASK;
- maskb ^= PyLong_MASK;
- negz = -1;
- }
+ negz = nega & negb;
+ size_z = negb ? size_a : size_b;
break;
case '|':
- if (maska || maskb) {
- op = '&';
- maska ^= PyLong_MASK;
- maskb ^= PyLong_MASK;
- negz = -1;
- }
+ negz = nega | negb;
+ size_z = negb ? size_b : size_a;
break;
+ default:
+ PyErr_BadArgument();
+ return NULL;
}
- /* JRH: The original logic here was to allocate the result value (z)
- as the longer of the two operands. However, there are some cases
- where the result is guaranteed to be shorter than that: AND of two
- positives, OR of two negatives: use the shorter number. AND with
- mixed signs: use the positive number. OR with mixed signs: use the
- negative number. After the transformations above, op will be '&'
- iff one of these cases applies, and mask will be non-0 for operands
- whose length should be ignored.
- */
-
- size_a = Py_SIZE(a);
- size_b = Py_SIZE(b);
- size_z = op == '&'
- ? (maska
- ? size_b
- : (maskb ? size_a : MIN(size_a, size_b)))
- : MAX(size_a, size_b);
- z = _PyLong_New(size_z);
+ /* We allow an extra digit if z is negative, to make sure that
+ the final two's complement of z doesn't overflow. */
+ z = _PyLong_New(size_z + negz);
if (z == NULL) {
Py_DECREF(a);
Py_DECREF(b);
return NULL;
}
- for (i = 0; i < size_z; ++i) {
- diga = (i < size_a ? a->ob_digit[i] : 0) ^ maska;
- digb = (i < size_b ? b->ob_digit[i] : 0) ^ maskb;
- switch (op) {
- case '&': z->ob_digit[i] = diga & digb; break;
- case '|': z->ob_digit[i] = diga | digb; break;
- case '^': z->ob_digit[i] = diga ^ digb; break;
- }
+ /* Compute digits for overlap of a and b. */
+ switch(op) {
+ case '&':
+ for (i = 0; i < size_b; ++i)
+ z->ob_digit[i] = a->ob_digit[i] & b->ob_digit[i];
+ break;
+ case '|':
+ for (i = 0; i < size_b; ++i)
+ z->ob_digit[i] = a->ob_digit[i] | b->ob_digit[i];
+ break;
+ case '^':
+ for (i = 0; i < size_b; ++i)
+ z->ob_digit[i] = a->ob_digit[i] ^ b->ob_digit[i];
+ break;
+ default:
+ PyErr_BadArgument();
+ return NULL;
+ }
+
+ /* Copy any remaining digits of a, inverting if necessary. */
+ if (op == '^' && negb)
+ for (; i < size_z; ++i)
+ z->ob_digit[i] = a->ob_digit[i] ^ PyLong_MASK;
+ else if (i < size_z)
+ memcpy(&z->ob_digit[i], &a->ob_digit[i],
+ (size_z-i)*sizeof(digit));
+
+ /* Complement result if negative. */
+ if (negz) {
+ Py_SIZE(z) = -(Py_SIZE(z));
+ z->ob_digit[size_z] = PyLong_MASK;
+ v_complement(z->ob_digit, z->ob_digit, size_z+1);
}
Py_DECREF(a);
Py_DECREF(b);
- z = long_normalize(z);
- if (negz == 0)
- return (PyObject *) z;
- v = long_invert(z);
- Py_DECREF(z);
- return v;
+ return (PyObject *)long_normalize(z);
}
static PyObject *
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