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#ifndef Py_INTERNAL_OBJECT_STACK_H

#define Py_INTERNAL_OBJECT_STACK_H

#ifdef __cplusplus

extern "C" {

#endif

#ifndef Py_BUILD_CORE

# error "this header requires Py_BUILD_CORE define"

#endif

// _PyObjectStack is a stack of Python objects implemented as a linked list of

// fixed size buffers.

// Chosen so that _PyObjectStackChunk is a power-of-two size.

#define _Py_OBJECT_STACK_CHUNK_SIZE 254

typedef struct _PyObjectStackChunk {

struct _PyObjectStackChunk *prev;

Py_ssize_t n;

PyObject *objs[_Py_OBJECT_STACK_CHUNK_SIZE];

} _PyObjectStackChunk;

typedef struct _PyObjectStack {

_PyObjectStackChunk *head;

} _PyObjectStack;

extern _PyObjectStackChunk *

_PyObjectStackChunk_New(void);

extern void

_PyObjectStackChunk_Free(_PyObjectStackChunk *);

// Push an item onto the stack. Return -1 on allocation failure, 0 on success.

static inline int

_PyObjectStack_Push(_PyObjectStack *stack, PyObject *obj)

{

_PyObjectStackChunk *buf = stack->head;

if (buf == NULL || buf->n == _Py_OBJECT_STACK_CHUNK_SIZE) {

buf = _PyObjectStackChunk_New();

if (buf == NULL) {

return -1;

}

buf->prev = stack->head;

buf->n = 0;

stack->head = buf;

}

assert(buf->n >= 0 && buf->n < _Py_OBJECT_STACK_CHUNK_SIZE);

buf->objs[buf->n] = obj;

buf->n++;

return 0;

}

// Pop the top item from the stack. Return NULL if the stack is empty.

static inline PyObject *

_PyObjectStack_Pop(_PyObjectStack *stack)

{

_PyObjectStackChunk *buf = stack->head;

if (buf == NULL) {

return NULL;

}

assert(buf->n > 0 && buf->n <= _Py_OBJECT_STACK_CHUNK_SIZE);

buf->n--;

PyObject *obj = buf->objs[buf->n];

if (buf->n == 0) {

stack->head = buf->prev;

_PyObjectStackChunk_Free(buf);

}

return obj;

}

static inline Py_ssize_t

_PyObjectStack_Size(_PyObjectStack *stack)

{

Py_ssize_t size = 0;

for (_PyObjectStackChunk *buf = stack->head; buf != NULL; buf = buf->prev) {

size += buf->n;

}

return size;

}

// Merge src into dst, leaving src empty

extern void

_PyObjectStack_Merge(_PyObjectStack *dst, _PyObjectStack *src);

// Remove all items from the stack

extern void

_PyObjectStack_Clear(_PyObjectStack *stack);

#ifdef __cplusplus

}

#endif

#endif // !Py_INTERNAL_OBJECT_STACK_H

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