cpython/Modules/_collectionsmodule.c at dd407d5006809646ff42ef1b120c67dc794418cf · pythoncapi/cpython

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#include "Python.h"

#include "structmember.h"

#ifdef STDC_HEADERS

#include <stddef.h>

#else

#include <sys/types.h> /* For size_t */

#endif

/* collections module implementation of a deque() datatype

Written and maintained by Raymond D. Hettinger <python@rcn.com>

/* The block length may be set to any number over 1. Larger numbers

* reduce the number of calls to the memory allocator, give faster

* indexing and rotation, and reduce the link to data overhead ratio.

* Making the block length a power of two speeds-up the modulo

* and division calculations in deque_item() and deque_ass_item().

#define BLOCKLEN 64

#define CENTER ((BLOCKLEN - 1) / 2)

/* Data for deque objects is stored in a doubly-linked list of fixed

* length blocks. This assures that appends or pops never move any

* other data elements besides the one being appended or popped.

* Another advantage is that it completely avoids use of realloc(),

* resulting in more predictable performance.

* Textbook implementations of doubly-linked lists store one datum

* per link, but that gives them a 200% memory overhead (a prev and

* next link for each datum) and it costs one malloc() call per data

* element. By using fixed-length blocks, the link to data ratio is

* significantly improved and there are proportionally fewer calls

* to malloc() and free(). The data blocks of consecutive pointers

* also improve cache locality.

* The list of blocks is never empty, so d.leftblock and d.rightblock

* are never equal to NULL. The list is not circular.

* A deque d's first element is at d.leftblock[leftindex]

* and its last element is at d.rightblock[rightindex].

* Unlike Python slice indices, these indices are inclusive on both

* ends. This makes the algorithms for left and right operations

* more symmetrical and it simplifies the design.

* The indices, d.leftindex and d.rightindex are always in the range:

* 0 <= index < BLOCKLEN

* And their exact relationship is:

* (d.leftindex + d.len - 1) % BLOCKLEN == d.rightindex

* Whenever d.leftblock == d.rightblock, then:

* d.leftindex + d.len - 1 == d.rightindex

* However, when d.leftblock != d.rightblock, the d.leftindex and

* d.rightindex become indices into distinct blocks and either may

* be larger than the other.

* Empty deques have:

* d.len == 0

* d.leftblock == d.rightblock

* d.leftindex == CENTER + 1

* d.rightindex == CENTER

* Checking for d.len == 0 is the intended way to see whether d is empty.

typedef struct BLOCK {

struct BLOCK *leftlink;

PyObject *data[BLOCKLEN];

struct BLOCK *rightlink;

} block;

typedef struct {

PyObject_VAR_HEAD

block *leftblock;

block *rightblock;

Py_ssize_t leftindex; /* 0 <= leftindex < BLOCKLEN */

Py_ssize_t rightindex; /* 0 <= rightindex < BLOCKLEN */

size_t state; /* incremented whenever the indices move */

Py_ssize_t maxlen; /* maxlen is -1 for unbounded deques */

PyObject *weakreflist;

} dequeobject;

static PyTypeObject deque_type;

/* For debug builds, add error checking to track the endpoints

* in the chain of links. The goal is to make sure that link

* assignments only take place at endpoints so that links already

* in use do not get overwritten.

* CHECK_END should happen before each assignment to a block's link field.

* MARK_END should happen whenever a link field becomes a new endpoint.

* This happens when new blocks are added or whenever an existing

* block is freed leaving another existing block as the new endpoint.

#ifndef NDEBUG

#define MARK_END(link) link = NULL;

#define CHECK_END(link) assert(link == NULL);

#define CHECK_NOT_END(link) assert(link != NULL);

#else

#define MARK_END(link)

#define CHECK_END(link)

#define CHECK_NOT_END(link)

#endif

/* A simple freelisting scheme is used to minimize calls to the memory

allocator. It accommodates common use cases where new blocks are being

added at about the same rate as old blocks are being freed.

#define MAXFREEBLOCKS 16

static Py_ssize_t numfreeblocks = 0;

static block *freeblocks[MAXFREEBLOCKS];

static block *

newblock(void) {

block *b;

if (numfreeblocks) {

numfreeblocks--;

return freeblocks[numfreeblocks];

}

b = PyMem_Malloc(sizeof(block));

if (b != NULL) {

return b;

}

PyErr_NoMemory();

return NULL;

}

static void

freeblock(block *b)

{

if (numfreeblocks < MAXFREEBLOCKS) {

freeblocks[numfreeblocks] = b;

numfreeblocks++;

} else {

PyMem_Free(b);

}

static PyObject *

deque_new(PyTypeObject *type, PyObject *args, PyObject *kwds)

{

dequeobject *deque;

block *b;

/* create dequeobject structure */

deque = (dequeobject *)type->tp_alloc(type, 0);

if (deque == NULL)

return NULL;

b = newblock();

if (b == NULL) {

Py_DECREF(deque);

return NULL;

}

MARK_END(b->leftlink);

MARK_END(b->rightlink);

assert(BLOCKLEN >= 2);

Py_SIZE(deque) = 0;

deque->leftblock = b;

deque->rightblock = b;

deque->leftindex = CENTER + 1;

deque->rightindex = CENTER;

deque->state = 0;

deque->maxlen = -1;

deque->weakreflist = NULL;

return (PyObject *)deque;

}

static PyObject *

deque_pop(dequeobject *deque, PyObject *unused)

{

PyObject *item;

block *prevblock;

if (Py_SIZE(deque) == 0) {

PyErr_SetString(PyExc_IndexError, "pop from an empty deque");

return NULL;

}

item = deque->rightblock->data[deque->rightindex];

deque->rightindex--;

Py_SIZE(deque)--;

deque->state++;

if (deque->rightindex < 0) {

if (Py_SIZE(deque)) {

prevblock = deque->rightblock->leftlink;

assert(deque->leftblock != deque->rightblock);

freeblock(deque->rightblock);

CHECK_NOT_END(prevblock);

MARK_END(prevblock->rightlink);

deque->rightblock = prevblock;

deque->rightindex = BLOCKLEN - 1;

} else {

assert(deque->leftblock == deque->rightblock);

assert(deque->leftindex == deque->rightindex+1);

/* re-center instead of freeing a block */

deque->leftindex = CENTER + 1;

deque->rightindex = CENTER;

}

return item;

}

PyDoc_STRVAR(pop_doc, "Remove and return the rightmost element.");

static PyObject *

deque_popleft(dequeobject *deque, PyObject *unused)

{

PyObject *item;

block *prevblock;

if (Py_SIZE(deque) == 0) {

PyErr_SetString(PyExc_IndexError, "pop from an empty deque");

return NULL;

}

assert(deque->leftblock != NULL);

item = deque->leftblock->data[deque->leftindex];

deque->leftindex++;

Py_SIZE(deque)--;

deque->state++;

if (deque->leftindex == BLOCKLEN) {

if (Py_SIZE(deque)) {

assert(deque->leftblock != deque->rightblock);

prevblock = deque->leftblock->rightlink;

freeblock(deque->leftblock);

CHECK_NOT_END(prevblock);

MARK_END(prevblock->leftlink);

deque->leftblock = prevblock;

deque->leftindex = 0;

} else {

assert(deque->leftblock == deque->rightblock);

assert(deque->leftindex == deque->rightindex+1);

/* re-center instead of freeing a block */

deque->leftindex = CENTER + 1;

deque->rightindex = CENTER;

}

return item;

}

PyDoc_STRVAR(popleft_doc, "Remove and return the leftmost element.");

/* The deque's size limit is d.maxlen. The limit can be zero or positive.

* If there is no limit, then d.maxlen == -1.

* After an item is added to a deque, we check to see if the size has

* grown past the limit. If it has, we get the size back down to the limit

* by popping an item off of the opposite end. The methods that can

* trigger this are append(), appendleft(), extend(), and extendleft().

* The macro to check whether a deque needs to be trimmed uses a single

* unsigned test that returns true whenever 0 <= maxlen < Py_SIZE(deque).

#define NEEDS_TRIM(deque, maxlen) ((size_t)(maxlen) < (size_t)(Py_SIZE(deque)))

static int

deque_append_internal(dequeobject *deque, PyObject *item, Py_ssize_t maxlen)

{

if (deque->rightindex == BLOCKLEN - 1) {

block *b = newblock();

if (b == NULL)

return -1;

b->leftlink = deque->rightblock;

CHECK_END(deque->rightblock->rightlink);

deque->rightblock->rightlink = b;

deque->rightblock = b;

MARK_END(b->rightlink);

deque->rightindex = -1;

}

Py_SIZE(deque)++;

deque->rightindex++;

deque->rightblock->data[deque->rightindex] = item;

if (NEEDS_TRIM(deque, maxlen)) {

PyObject *olditem = deque_popleft(deque, NULL);

Py_DECREF(olditem);

} else {

deque->state++;

}

return 0;

}

static PyObject *

deque_append(dequeobject *deque, PyObject *item)

{

Py_INCREF(item);

if (deque_append_internal(deque, item, deque->maxlen) < 0)

return NULL;

Py_RETURN_NONE;

}

PyDoc_STRVAR(append_doc, "Add an element to the right side of the deque.");

static int

deque_appendleft_internal(dequeobject *deque, PyObject *item, Py_ssize_t maxlen)

{

if (deque->leftindex == 0) {

block *b = newblock();

if (b == NULL)

return -1;

b->rightlink = deque->leftblock;

CHECK_END(deque->leftblock->leftlink);

deque->leftblock->leftlink = b;

deque->leftblock = b;

MARK_END(b->leftlink);

deque->leftindex = BLOCKLEN;

}

Py_SIZE(deque)++;

deque->leftindex--;

deque->leftblock->data[deque->leftindex] = item;

if (NEEDS_TRIM(deque, deque->maxlen)) {

PyObject *olditem = deque_pop(deque, NULL);

Py_DECREF(olditem);

} else {

deque->state++;

}

return 0;

}

static PyObject *

deque_appendleft(dequeobject *deque, PyObject *item)

{

Py_INCREF(item);

if (deque_appendleft_internal(deque, item, deque->maxlen) < 0)

return NULL;

Py_RETURN_NONE;

}

PyDoc_STRVAR(appendleft_doc, "Add an element to the left side of the deque.");

static PyObject*

finalize_iterator(PyObject *it)

{

if (PyErr_Occurred()) {

if (PyErr_ExceptionMatches(PyExc_StopIteration))

PyErr_Clear();

else {

Py_DECREF(it);

return NULL;

}

Py_DECREF(it);

Py_RETURN_NONE;

}

/* Run an iterator to exhaustion. Shortcut for

the extend/extendleft methods when maxlen == 0. */

static PyObject*

consume_iterator(PyObject *it)

{

PyObject *(*iternext)(PyObject *);

PyObject *item;

iternext = *Py_TYPE(it)->tp_iternext;

while ((item = iternext(it)) != NULL) {

Py_DECREF(item);

}

return finalize_iterator(it);

}

static PyObject *

deque_extend(dequeobject *deque, PyObject *iterable)

{

PyObject *it, *item;

PyObject *(*iternext)(PyObject *);

Py_ssize_t maxlen = deque->maxlen;

/* Handle case where id(deque) == id(iterable) */

if ((PyObject *)deque == iterable) {

PyObject *result;

PyObject *s = PySequence_List(iterable);

if (s == NULL)

return NULL;

result = deque_extend(deque, s);

Py_DECREF(s);

return result;

}

it = PyObject_GetIter(iterable);

if (it == NULL)

return NULL;

if (maxlen == 0)

return consume_iterator(it);

/* Space saving heuristic. Start filling from the left */

if (Py_SIZE(deque) == 0) {

assert(deque->leftblock == deque->rightblock);

assert(deque->leftindex == deque->rightindex+1);

deque->leftindex = 1;

deque->rightindex = 0;

}

iternext = *Py_TYPE(it)->tp_iternext;

while ((item = iternext(it)) != NULL) {

if (deque->rightindex == BLOCKLEN - 1) {

block *b = newblock();

if (b == NULL) {

Py_DECREF(item);

Py_DECREF(it);

return NULL;

}

b->leftlink = deque->rightblock;

CHECK_END(deque->rightblock->rightlink);

deque->rightblock->rightlink = b;

deque->rightblock = b;

MARK_END(b->rightlink);

deque->rightindex = -1;

}

Py_SIZE(deque)++;

deque->rightindex++;

deque->rightblock->data[deque->rightindex] = item;

if (NEEDS_TRIM(deque, maxlen)) {

PyObject *olditem = deque_popleft(deque, NULL);

Py_DECREF(olditem);

} else {

deque->state++;

}

return finalize_iterator(it);

}

PyDoc_STRVAR(extend_doc,

"Extend the right side of the deque with elements from the iterable");

static PyObject *

deque_extendleft(dequeobject *deque, PyObject *iterable)

{

PyObject *it, *item;

PyObject *(*iternext)(PyObject *);

Py_ssize_t maxlen = deque->maxlen;

/* Handle case where id(deque) == id(iterable) */

if ((PyObject *)deque == iterable) {

PyObject *result;

PyObject *s = PySequence_List(iterable);

if (s == NULL)

return NULL;

result = deque_extendleft(deque, s);

Py_DECREF(s);

return result;

}

it = PyObject_GetIter(iterable);

if (it == NULL)

return NULL;

if (maxlen == 0)

return consume_iterator(it);

/* Space saving heuristic. Start filling from the right */

if (Py_SIZE(deque) == 0) {

assert(deque->leftblock == deque->rightblock);

assert(deque->leftindex == deque->rightindex+1);

deque->leftindex = BLOCKLEN - 1;

deque->rightindex = BLOCKLEN - 2;

}

iternext = *Py_TYPE(it)->tp_iternext;

while ((item = iternext(it)) != NULL) {

if (deque->leftindex == 0) {

block *b = newblock();

if (b == NULL) {

Py_DECREF(item);

Py_DECREF(it);

return NULL;

}

b->rightlink = deque->leftblock;

CHECK_END(deque->leftblock->leftlink);

deque->leftblock->leftlink = b;

deque->leftblock = b;

MARK_END(b->leftlink);

deque->leftindex = BLOCKLEN;

}

Py_SIZE(deque)++;

deque->leftindex--;

deque->leftblock->data[deque->leftindex] = item;

if (NEEDS_TRIM(deque, maxlen)) {

PyObject *olditem = deque_pop(deque, NULL);

Py_DECREF(olditem);

} else {

deque->state++;

}

return finalize_iterator(it);

}

PyDoc_STRVAR(extendleft_doc,

"Extend the left side of the deque with elements from the iterable");

static PyObject *

deque_inplace_concat(dequeobject *deque, PyObject *other)

{

PyObject *result;

result = deque_extend(deque, other);

if (result == NULL)

return result;

Py_INCREF(deque);

Py_DECREF(result);

return (PyObject *)deque;

}

static PyObject *

deque_copy(PyObject *deque)

{

dequeobject *old_deque = (dequeobject *)deque;

if (Py_TYPE(deque) == &deque_type) {

dequeobject *new_deque;

PyObject *rv;

new_deque = (dequeobject *)deque_new(&deque_type, (PyObject *)NULL, (PyObject *)NULL);

if (new_deque == NULL)

return NULL;

new_deque->maxlen = old_deque->maxlen;

/* Fast path for the deque_repeat() common case where len(deque) == 1 */

if (Py_SIZE(deque) == 1) {

PyObject *item = old_deque->leftblock->data[old_deque->leftindex];

rv = deque_append(new_deque, item);

} else {

rv = deque_extend(new_deque, deque);

}

if (rv != NULL) {

Py_DECREF(rv);

return (PyObject *)new_deque;

}

Py_DECREF(new_deque);

return NULL;

}

if (old_deque->maxlen < 0)

return PyObject_CallFunctionObjArgs((PyObject *)(Py_TYPE(deque)),

deque, NULL);

else

return PyObject_CallFunction((PyObject *)(Py_TYPE(deque)), "Oi",

deque, old_deque->maxlen, NULL);

}

PyDoc_STRVAR(copy_doc, "Return a shallow copy of a deque.");

static PyObject *

deque_concat(dequeobject *deque, PyObject *other)

{

PyObject *new_deque, *result;

int rv;

rv = PyObject_IsInstance(other, (PyObject *)&deque_type);

if (rv <= 0) {

if (rv == 0) {

PyErr_Format(PyExc_TypeError,

"can only concatenate deque (not \"%.200s\") to deque",

other->ob_type->tp_name);

}

return NULL;

}

new_deque = deque_copy((PyObject *)deque);

if (new_deque == NULL)

return NULL;

result = deque_extend((dequeobject *)new_deque, other);

if (result == NULL) {

Py_DECREF(new_deque);

return NULL;

}

Py_DECREF(result);

return new_deque;

}

static void

deque_clear(dequeobject *deque)

{

block *b;

block *prevblock;

block *leftblock;

Py_ssize_t leftindex;

Py_ssize_t n, m;

PyObject *item;

PyObject **itemptr, **limit;

if (Py_SIZE(deque) == 0)

return;

/* During the process of clearing a deque, decrefs can cause the

deque to mutate. To avoid fatal confusion, we have to make the

deque empty before clearing the blocks and never refer to

anything via deque->ref while clearing. (This is the same

technique used for clearing lists, sets, and dicts.)

Making the deque empty requires allocating a new empty block. In

the unlikely event that memory is full, we fall back to an

alternate method that doesn't require a new block. Repeating

pops in a while-loop is slower, possibly re-entrant (and a clever

adversary could cause it to never terminate).

b = newblock();

if (b == NULL) {

PyErr_Clear();

goto alternate_method;

}

/* Remember the old size, leftblock, and leftindex */

n = Py_SIZE(deque);

leftblock = deque->leftblock;

leftindex = deque->leftindex;

/* Set the deque to be empty using the newly allocated block */

MARK_END(b->leftlink);

MARK_END(b->rightlink);

Py_SIZE(deque) = 0;

deque->leftblock = b;

deque->rightblock = b;

deque->leftindex = CENTER + 1;

deque->rightindex = CENTER;

deque->state++;

/* Now the old size, leftblock, and leftindex are disconnected from

the empty deque and we can use them to decref the pointers.

m = (BLOCKLEN - leftindex > n) ? n : BLOCKLEN - leftindex;

itemptr = &leftblock->data[leftindex];

limit = itemptr + m;

n -= m;

while (1) {

if (itemptr == limit) {

if (n == 0)

break;

CHECK_NOT_END(leftblock->rightlink);

prevblock = leftblock;

leftblock = leftblock->rightlink;

m = (n > BLOCKLEN) ? BLOCKLEN : n;

itemptr = leftblock->data;

limit = itemptr + m;

n -= m;

freeblock(prevblock);

}

item = *(itemptr++);

Py_DECREF(item);

}

CHECK_END(leftblock->rightlink);

freeblock(leftblock);

return;

alternate_method:

while (Py_SIZE(deque)) {

item = deque_pop(deque, NULL);

assert (item != NULL);

Py_DECREF(item);

}

static PyObject *

deque_clearmethod(dequeobject *deque)

{

deque_clear(deque);

Py_RETURN_NONE;

}

PyDoc_STRVAR(clear_doc, "Remove all elements from the deque.");

static PyObject *

deque_inplace_repeat(dequeobject *deque, Py_ssize_t n)

{

Py_ssize_t i, m, size;

PyObject *seq;

PyObject *rv;

size = Py_SIZE(deque);

if (size == 0 || n == 1) {

Py_INCREF(deque);

return (PyObject *)deque;

}

if (n <= 0) {

deque_clear(deque);

Py_INCREF(deque);

return (PyObject *)deque;

}

if (size == 1) {

/* common case, repeating a single element */

PyObject *item = deque->leftblock->data[deque->leftindex];

if (deque->maxlen >= 0 && n > deque->maxlen)

n = deque->maxlen;

deque->state++;

for (i = 0 ; i < n-1 ; ) {

if (deque->rightindex == BLOCKLEN - 1) {

block *b = newblock();

if (b == NULL) {

Py_SIZE(deque) += i;

return NULL;

}

b->leftlink = deque->rightblock;

CHECK_END(deque->rightblock->rightlink);

deque->rightblock->rightlink = b;

deque->rightblock = b;

MARK_END(b->rightlink);

deque->rightindex = -1;

}

m = n - 1 - i;

if (m > BLOCKLEN - 1 - deque->rightindex)

m = BLOCKLEN - 1 - deque->rightindex;

i += m;

while (m--) {

deque->rightindex++;

Py_INCREF(item);

deque->rightblock->data[deque->rightindex] = item;

}

Py_SIZE(deque) += i;

Py_INCREF(deque);

return (PyObject *)deque;

}

if ((size_t)size > PY_SSIZE_T_MAX / (size_t)n) {

return PyErr_NoMemory();

}

seq = PySequence_List((PyObject *)deque);

if (seq == NULL)

return seq;

for (i = 0 ; i < n-1 ; i++) {

rv = deque_extend(deque, seq);

if (rv == NULL) {

Py_DECREF(seq);

return NULL;

}

Py_DECREF(rv);

}

Py_INCREF(deque);

Py_DECREF(seq);

return (PyObject *)deque;

}

static PyObject *

deque_repeat(dequeobject *deque, Py_ssize_t n)

{

dequeobject *new_deque;

PyObject *rv;

new_deque = (dequeobject *)deque_copy((PyObject *) deque);

if (new_deque == NULL)

return NULL;

rv = deque_inplace_repeat(new_deque, n);

Py_DECREF(new_deque);

return rv;

}

/* The rotate() method is part of the public API and is used internally

as a primitive for other methods.

Rotation by 1 or -1 is a common case, so any optimizations for high

volume rotations should take care not to penalize the common case.

Conceptually, a rotate by one is equivalent to a pop on one side and an

append on the other. However, a pop/append pair is unnecessarily slow

because it requires an incref/decref pair for an object located randomly

in memory. It is better to just move the object pointer from one block

to the next without changing the reference count.

When moving batches of pointers, it is tempting to use memcpy() but that

proved to be slower than a simple loop for a variety of reasons.

Memcpy() cannot know in advance that we're copying pointers instead of

bytes, that the source and destination are pointer aligned and

non-overlapping, that moving just one pointer is a common case, that we

never need to move more than BLOCKLEN pointers, and that at least one

pointer is always moved.

For high volume rotations, newblock() and freeblock() are never called

more than once. Previously emptied blocks are immediately reused as a

destination block. If a block is left-over at the end, it is freed.

static int

_deque_rotate(dequeobject *deque, Py_ssize_t n)

{

block *b = NULL;

block *leftblock = deque->leftblock;

block *rightblock = deque->rightblock;

Py_ssize_t leftindex = deque->leftindex;

Py_ssize_t rightindex = deque->rightindex;

Py_ssize_t len=Py_SIZE(deque), halflen=len>>1;

int rv = -1;

if (len <= 1)

return 0;

if (n > halflen || n < -halflen) {

n %= len;

if (n > halflen)

n -= len;

else if (n < -halflen)

n += len;

}

assert(len > 1);

assert(-halflen <= n && n <= halflen);

deque->state++;

while (n > 0) {

if (leftindex == 0) {

if (b == NULL) {

b = newblock();

if (b == NULL)

goto done;

}

b->rightlink = leftblock;

CHECK_END(leftblock->leftlink);

leftblock->leftlink = b;

leftblock = b;

MARK_END(b->leftlink);

leftindex = BLOCKLEN;

b = NULL;

}

assert(leftindex > 0);

{

PyObject **src, **dest;

Py_ssize_t m = n;

if (m > rightindex + 1)

m = rightindex + 1;

if (m > leftindex)

m = leftindex;

assert (m > 0 && m <= len);

rightindex -= m;

leftindex -= m;

src = &rightblock->data[rightindex + 1];

dest = &leftblock->data[leftindex];

n -= m;

do {

*(dest++) = *(src++);

} while (--m);

}

if (rightindex < 0) {

assert(leftblock != rightblock);

assert(b == NULL);

b = rightblock;

CHECK_NOT_END(rightblock->leftlink);

rightblock = rightblock->leftlink;

MARK_END(rightblock->rightlink);

rightindex = BLOCKLEN - 1;

}

while (n < 0) {

if (rightindex == BLOCKLEN - 1) {

if (b == NULL) {

b = newblock();

if (b == NULL)

goto done;

}

b->leftlink = rightblock;

CHECK_END(rightblock->rightlink);

rightblock->rightlink = b;

rightblock = b;

MARK_END(b->rightlink);

rightindex = -1;

b = NULL;

}

assert (rightindex < BLOCKLEN - 1);

{

PyObject **src, **dest;

Py_ssize_t m = -n;

if (m > BLOCKLEN - leftindex)

m = BLOCKLEN - leftindex;

if (m > BLOCKLEN - 1 - rightindex)

m = BLOCKLEN - 1 - rightindex;

assert (m > 0 && m <= len);

src = &leftblock->data[leftindex];

dest = &rightblock->data[rightindex + 1];

leftindex += m;

rightindex += m;

n += m;

do {

*(dest++) = *(src++);

} while (--m);

}

if (leftindex == BLOCKLEN) {

assert(leftblock != rightblock);

assert(b == NULL);

b = leftblock;

CHECK_NOT_END(leftblock->rightlink);

leftblock = leftblock->rightlink;

MARK_END(leftblock->leftlink);

leftindex = 0;

}

rv = 0;

done:

if (b != NULL)

freeblock(b);

deque->leftblock = leftblock;

deque->rightblock = rightblock;

deque->leftindex = leftindex;

deque->rightindex = rightindex;

return rv;

}

static PyObject *

deque_rotate(dequeobject *deque, PyObject **args, Py_ssize_t nargs,

PyObject *kwnames)

{

Py_ssize_t n=1;

if (!_PyArg_NoStackKeywords("rotate", kwnames)) {

return NULL;

}

if (!_PyArg_ParseStack(args, nargs, "|n:rotate", &n)) {

return NULL;

}

if (!_deque_rotate(deque, n))

Py_RETURN_NONE;

return NULL;

}

PyDoc_STRVAR(rotate_doc,

"Rotate the deque n steps to the right (default n=1). If n is negative, rotates left.");

static PyObject *

deque_reverse(dequeobject *deque, PyObject *unused)

{

block *leftblock = deque->leftblock;

block *rightblock = deque->rightblock;

Py_ssize_t leftindex = deque->leftindex;

Py_ssize_t rightindex = deque->rightindex;

Py_ssize_t n = Py_SIZE(deque) >> 1;

PyObject *tmp;

n++;

while (--n) {

/* Validate that pointers haven't met in the middle */

assert(leftblock != rightblock || leftindex < rightindex);

CHECK_NOT_END(leftblock);

CHECK_NOT_END(rightblock);

/* Swap */

tmp = leftblock->data[leftindex];

leftblock->data[leftindex] = rightblock->data[rightindex];

rightblock->data[rightindex] = tmp;

/* Advance left block/index pair */

leftindex++;

if (leftindex == BLOCKLEN) {

leftblock = leftblock->rightlink;

leftindex = 0;

}

/* Step backwards with the right block/index pair */

rightindex--;

if (rightindex < 0) {

rightblock = rightblock->leftlink;

rightindex = BLOCKLEN - 1;

}

Py_RETURN_NONE;

}

PyDoc_STRVAR(reverse_doc,

"D.reverse() -- reverse *IN PLACE*");

static PyObject *

deque_count(dequeobject *deque, PyObject *v)

{

block *b = deque->leftblock;

Py_ssize_t index = deque->leftindex;

Py_ssize_t n = Py_SIZE(deque);

Py_ssize_t count = 0;

size_t start_state = deque->state;

PyObject *item;

int cmp;

n++;

while (--n) {

CHECK_NOT_END(b);

item = b->data[index];

cmp = PyObject_RichCompareBool(item, v, Py_EQ);

if (cmp < 0)

return NULL;

count += cmp;

if (start_state != deque->state) {

PyErr_SetString(PyExc_RuntimeError,

"deque mutated during iteration");

return NULL;

}

/* Advance left block/index pair */

index++;

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