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Issue #1087418: Small performance boost for bitwise operations on longs. 

Initial patch by Gregory Smith;  some tweaks added.
This commit is contained in:
Mark Dickinson 2009-10-25 20:39:06 +00:00
parent f1ca811abb
commit 8d87dc0c29
2 changed files with 103 additions and 67 deletions
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2
Misc/NEWS
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@ -12,6 +12,8 @@ What's New in Python 2.7 alpha 1
Core and Builtins
-----------------
- Issue #1087418: Boost performance of bitwise operations for longs.
- Issue #1722344: threading._shutdown() is now called in Py_Finalize(), which
fixes the problem of some exceptions being thrown at shutdown when the
interpreter is killed. Patch by Adam Olsen.

168
Objects/longobject.c
View File

@ -3411,6 +3411,22 @@ lshift_error:
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 */
@ -3419,60 +3435,49 @@ long_bitwise(PyLongObject *a,
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;
}
negz = 0;
switch (op) {
case '^':
if (maska != maskb) {
maska ^= PyLong_MASK;
negz = -1;
}
break;
case '&':
if (maska && maskb) {
op = '|';
maska ^= PyLong_MASK;
maskb ^= PyLong_MASK;
negz = -1;
}
break;
case '|':
if (maska || maskb) {
op = '&';
maska ^= PyLong_MASK;
maskb ^= PyLong_MASK;
negz = -1;
}
break;
/* 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;
}
/* JRH: The original logic here was to allocate the result value (z)
@ -3480,43 +3485,72 @@ long_bitwise(PyLongObject *a,
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.
negative number.
*/
switch (op) {
case '^':
negz = nega ^ negb;
size_z = size_a;
break;
case '&':
negz = nega & negb;
size_z = negb ? size_a : size_b;
break;
case '|':
negz = nega | negb;
size_z = negb ? size_b : size_a;
break;
default:
PyErr_BadArgument();
return NULL;
}
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 *