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/*
* This file is part of the Green End SFTP Server.
* Copyright (C) 2007, 2011, 2014 Richard Kettlewell
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*/
/** @file alloc.c @brief Allocator implementation */
#include "sftpserver.h"
#include "alloc.h"
#include "utils.h"
#include "debug.h"
#include <stdlib.h>
#include <assert.h>
#include <string.h>
union block;
/** @brief One chunk in an allocator
*
* A chunk is a contiguous region of memory, divided into @ref block objects,
* supporting efficient allocation.
*/
struct chunk {
/** @brief Next chunk */
struct chunk *next;
/** @brief Pointer to next allocatable block */
union block *ptr;
/** @brief Number of blocks left in this chunk */
size_t left;
/** @brief Padding
*
* size_t will usually have the same size as a pointer; by chucking an extra
* one in we become 4 * the size of a pointer, which is much more likely to
* be a power of 2 than 3 *.
*/
size_t spare;
};
/** @brief Alignment block for an allocator
*/
union block {
int i;
long l;
float f;
double d;
void *vp;
double *ip;
int (*fnp)(void);
struct chunk c;
};
/** @brief Default number of blocks in a new chunk
*
* A chunk may be bigger than this if a large allocation was requested.
*/
#define NBLOCKS 512
struct allocator *sftp_alloc_init(struct allocator *a) {
a->chunks = 0;
return a;
}
/** @brief Convert @p nbytes to a block count
* @param nbytes Number of bytes
* @return Number of blocks necessary to contain @p nbytes
*/
static inline size_t blocks(size_t nbytes) {
return nbytes / sizeof(union block) + !!(nbytes % sizeof(union block));
}
void *sftp_alloc(struct allocator *a, size_t n) {
/* calculate number of blocks */
const size_t m = blocks(n);
struct chunk *c;
if(!m)
return 0;
assert(a != 0);
assert(m != SIZE_MAX); /* ...and so m+1 > 0 */
/* See if there's enough room */
if(!(c = a->chunks) || c->left < m) {
/* Make sure we allocate enough space */
const size_t cs = m >= NBLOCKS ? m + 1 : NBLOCKS;
/* sftp_xcalloc -> calloc which 0-fills */
union block *nb;
nb = sftp_xcalloc(cs, sizeof(union block));
c = &nb->c;
c->next = a->chunks;
c->ptr = nb + 1;
c->left = cs - 1;
a->chunks = c;
}
assert(m <= c->left);
/* We always return 0-filled memory. In this case we fill by block, which is
* guaranteed to be at least enough (compare below). */
sftp_memset(c->ptr, 0, m * sizeof(union block));
c->left -= m;
c->ptr += m;
return c->ptr - m;
}
void *sftp_alloc_more(struct allocator *a, void *ptr, size_t oldn,
size_t newn) {
const size_t oldm = blocks(oldn), newm = blocks(newn);
void *newptr;
if(ptr) {
assert(a->chunks != 0);
D(("ptr=%p oldm=%zu a->chunks->ptr=%p blocksize=%zu", ptr, oldm,
a->chunks->ptr, sizeof(union block)));
if((union block *)ptr + oldm == a->chunks->ptr) {
/* ptr is the most recently allocated block. We could do better and
* search all the chunks for it. */
if(newm <= oldm) {
/* We can always shrink. We capture the no-change case here too. */
a->chunks->ptr -= oldm - newm;
a->chunks->left += oldm - newm;
return ptr;
} else if(a->chunks->left >= newm - oldm) {
/* There is space to expand */
a->chunks->ptr += newm - oldm;
a->chunks->left -= newm - oldm;
/* 0-fill the new space. Note that we do this in byte terms (compare
* above), to deal with the case where the allocation shrinks by (say)
* a single non-zero byte but then expands again. */
sftp_memset((char *)ptr + oldn, 0, newn - oldn);
return ptr;
}
/* If we get here then we are expanding but there is not enough space to
* do so in the same chunk */
} else if(newm == oldm) {
/* This is not the most recently block but we're not changing its size
* anyway */
return ptr;
}
/* We have no choice but to allocate new space */
newptr = sftp_alloc(a, newn);
sftp_memcpy(newptr, ptr, oldn);
return newptr;
} else
/* There was no old allocation, just create a new one the easy way */
return sftp_alloc(a, newn);
}
void sftp_alloc_destroy(struct allocator *a) {
struct chunk *c, *d;
c = a->chunks;
while((d = c)) {
c = c->next;
free(d);
}
a->chunks = 0;
}
/*
Local Variables:
c-basic-offset:2
comment-column:40
fill-column:79
indent-tabs-mode:nil
End:
*/
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