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#include "stack.h"
#include <string.h>

int
stack_grow(struct stack *st, size_t new_size)
{
void **new_st;

if (st->asize >= new_size)
return 0;

new_st = realloc(st->item, new_size * sizeof(void *));
if (new_st == NULL)
return -1;

memset(new_st + st->asize, 0x0,
(new_size - st->asize) * sizeof(void *));

st->item = new_st;
st->asize = new_size;

if (st->size > new_size)
st->size = new_size;

return 0;
}

void
stack_free(struct stack *st)
{
if (!st)
return;

free(st->item);

st->item = NULL;
st->size = 0;
st->asize = 0;
}

int
stack_init(struct stack *st, size_t initial_size)
{
st->item = NULL;
st->size = 0;
st->asize = 0;

if (!initial_size)
initial_size = 8;

return stack_grow(st, initial_size);
}

void *
stack_pop(struct stack *st)
{
if (!st->size)
return NULL;

return st->item[--st->size];
}

int
stack_push(struct stack *st, void *item)
{
if (stack_grow(st, st->size * 2) < 0)
return -1;

st->item[st->size++] = item;
return 0;
}

void *
stack_top(struct stack *st)
{
if (!st->size)
return NULL;

return st->item[st->size - 1];
}

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