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Simplify random_seed to use _PyLong_AsByteArray. Closes issue #16496.

This commit is contained in:
Mark Dickinson 2012-12-21 21:52:49 +00:00
parent 1724bb196a
commit 4cd60175f1
1 changed files with 36 additions and 65 deletions
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101
Modules/_randommodule.c
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@ -168,9 +168,9 @@ init_genrand(RandomObject *self, unsigned long s)
/* init_key is the array for initializing keys */
/* key_length is its length */
static PyObject *
init_by_array(RandomObject *self, unsigned long init_key[], unsigned long key_length)
init_by_array(RandomObject *self, unsigned long init_key[], size_t key_length)
{
unsigned int i, j, k; /* was signed in the original code. RDH 12/16/2002 */
size_t i, j, k; /* was signed in the original code. RDH 12/16/2002 */
unsigned long *mt;
mt = self->state;
@ -207,14 +207,11 @@ static PyObject *
random_seed(RandomObject *self, PyObject *args)
{
PyObject *result = NULL; /* guilty until proved innocent */
PyObject *masklower = NULL;
PyObject *thirtytwo = NULL;
PyObject *n = NULL;
unsigned long *new_key, *key = NULL;
unsigned long keymax; /* # of allocated slots in key */
unsigned long keyused; /* # of used slots in key */
int err;
unsigned long *key = NULL;
unsigned char *key_as_bytes = NULL;
size_t bits, keyused, i;
int res;
PyObject *arg = NULL;
if (!PyArg_UnpackTuple(args, "seed", 0, 1, &arg))
@ -243,69 +240,43 @@ random_seed(RandomObject *self, PyObject *args)
if (n == NULL)
goto Done;
/* Now split n into 32-bit chunks, from the right. Each piece is
* stored into key, which has a capacity of keymax chunks, of which
* keyused are filled. Alas, the repeated shifting makes this a
* quadratic-time algorithm; we'd really like to use
* _PyLong_AsByteArray here, but then we'd have to break into the
* long representation to figure out how big an array was needed
* in advance.
*/
keymax = 8; /* arbitrary; grows later if needed */
keyused = 0;
key = (unsigned long *)PyMem_Malloc(keymax * sizeof(*key));
if (key == NULL)
/* Now split n into 32-bit chunks, from the right. */
bits = _PyLong_NumBits(n);
if (bits == (size_t)-1 && PyErr_Occurred())
goto Done;
masklower = PyLong_FromUnsignedLong(0xffffffffU);
if (masklower == NULL)
goto Done;
thirtytwo = PyLong_FromLong(32L);
if (thirtytwo == NULL)
goto Done;
while ((err=PyObject_IsTrue(n))) {
PyObject *newn;
PyObject *pychunk;
unsigned long chunk;
/* Figure out how many 32-bit chunks this gives us. */
keyused = bits == 0 ? 1 : (bits - 1) / 32 + 1;
if (err == -1)
goto Done;
pychunk = PyNumber_And(n, masklower);
if (pychunk == NULL)
goto Done;
chunk = PyLong_AsUnsignedLong(pychunk);
Py_DECREF(pychunk);
if (chunk == (unsigned long)-1 && PyErr_Occurred())
goto Done;
newn = PyNumber_Rshift(n, thirtytwo);
if (newn == NULL)
goto Done;
Py_DECREF(n);
n = newn;
if (keyused >= keymax) {
unsigned long bigger = keymax << 1;
if ((bigger >> 1) != keymax ||
bigger > PY_SSIZE_T_MAX / sizeof(*key)) {
PyErr_NoMemory();
goto Done;
}
new_key = (unsigned long *)PyMem_Realloc(key,
bigger * sizeof(*key));
if (new_key == NULL)
goto Done;
key = new_key;
keymax = bigger;
}
assert(keyused < keymax);
key[keyused++] = chunk;
/* Convert seed to byte sequence. */
key_as_bytes = (unsigned char *)PyMem_Malloc((size_t)4 * keyused);
if (key_as_bytes == NULL)
goto Done;
res = _PyLong_AsByteArray((PyLongObject *)n,
key_as_bytes, keyused * 4,
1, /* little-endian */
0); /* unsigned */
if (res == -1) {
PyMem_Free(key_as_bytes);
goto Done;
}
if (keyused == 0)
key[keyused++] = 0UL;
/* Fill array of unsigned longs from byte sequence. */
key = (unsigned long *)PyMem_Malloc(sizeof(unsigned long) * keyused);
if (key == NULL) {
PyMem_Free(key_as_bytes);
goto Done;
}
for (i = 0; i < keyused; i++) {
key[i] =
((unsigned long)key_as_bytes[4*i + 0] << 0) +
((unsigned long)key_as_bytes[4*i + 1] << 8) +
((unsigned long)key_as_bytes[4*i + 2] << 16) +
((unsigned long)key_as_bytes[4*i + 3] << 24);
}
PyMem_Free(key_as_bytes);
result = init_by_array(self, key, keyused);
Done:
Py_XDECREF(masklower);
Py_XDECREF(thirtytwo);
Py_XDECREF(n);
PyMem_Free(key);
return result;