pgpmempool.c

来自「著名的加密软件的应用于电子邮件中」· C语言 代码 · 共 214 行

/*
 * pgpMemPool.c - Pooled memory allocation, similar to GNU obstacks.
 *
 * Copyright (C) 1993-1997 Pretty Good Privacy, Inc. All rights reserved.
 *
 * Written by Colin Plumb.
 *
 * $Id: pgpMemPool.c,v 1.2.2.1 1997/06/07 09:50:34 mhw Exp $
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <string.h>

#include "pgpDebug.h"
#include "pgpMemPool.h"
#include "pgpMem.h"
#include "pgpUsuals.h"

#ifndef NULL
#define NULL 0
#endif

/* Define this symbol to cause secure wiping */
#ifndef SECURE
#define SECURE 1
#endif

/*
 * The memory pool allocation functions
 *
 * These are based on a linked list of memory blocks, usually of uniform
 * size. New memory is allocated from the tail of the current block,
 * until that is inadequate, then a new block is allocated.
 * The entire pool can be freed at once by calling memPoolFree().
 */

struct PoolBuf {
		struct PoolBuf *next;
		unsigned size;
		/* Data follows */
};

/* Page size to use */
#ifdef MSDOS
#define ALLOC_UNIT 1024
#else
#define ALLOC_UNIT 4096
#endif

static struct MemPool const EmptyPool =
		{ NULL, NULL, 0, ALLOC_UNIT, 0, (int (*)(void *))NULL, NULL};


/*
 * Initialize the pool for first use
 */
void
memPoolInit(struct MemPool *pool)
{
		*pool = EmptyPool;
}

/* Set the pool's purge function */
void
memPoolSetPurge(struct MemPool *pool, int (*purge)(void *), void *arg)
{
		pool->purge = purge;
		pool->purgearg = arg;
}

/*
 * Free all the memory in the pool
 */
void
memPoolEmpty(struct MemPool *pool)
{
		struct PoolBuf *buf;

		while ((buf = pool->head) != NULL) {
				pool->head = buf->next;
#if SECURE
				memset(buf, 0, buf->size);
#endif
				pgpMemFree(buf);
		}
		pool->freespace = 0;
		pool->totalsize = 0;
}


/*
 * Restore a pool to a marked position, freeing subsequently allocated
 * memory.
 */
void
memPoolCutBack(struct MemPool *pool, struct MemPool const *cutback)
{
		struct PoolBuf *buf;

		pgpAssert(pool);
		pgpAssert(cutback);

		pgpAssert(pool->totalsize >= cutback->totalsize);

		while((buf = pool->head) != cutback->head) {
				pool->head = buf->next;
#if SECURE
				memset(buf, 0, buf->size);
#endif
				pgpMemFree(buf);
		}
		*pool = *cutback;
}


/*
 * Structure and string allocations.
 * To make alingment work, strings and other objects
 * are allocated from different pools.
 */

/*
 * Allocate a chunk of memory for a structure, with the given alignment.
 * This is more space-efficient than malloc() for small objects
 * with loose alignment restrictions - like short strings.
 * Note that alignment is relative to the beginning of a chunk returned from
 * malloc(), which is guaranteed by ANSI to be as aligned as can possibly
 * matter.
 */
void *
memPoolAlloc(struct MemPool *pool, unsigned len, unsigned alignment)
{
		char *p;
		unsigned t;

		/* Where to allocate next object */
		p = pool->freeptr;
		/* How far it is from the beginning of the chunk. */
		t = p - (char *)pool->head;
		/*
		 * How much padding to add to freeptr to make alignment. The first
		 * case (not a power of 2) will never happen, but we do it right
		 * for bragging rights in the ANSI C compliance department.
		 */
		if (alignment & (alignment-1))
				t = alignment-1 - (t-1)%alignment;		/* Never called */
		else
				t = -t & (alignment-1);	/* This one always */

		/* Okay, does it fit? */
		if (pool->freespace >= len+t) {
				pool->freespace -= len+t;
				p += t;
				pool->freeptr = p + len;
				return p;
		}

		/* It does not fit in the current chunk. Allocate a new chunk. */

		/* First, figure out how padding is needed after the header. */
		if (alignment & (alignment-1))
				alignment -= 1 + (sizeof(struct PoolBuf)-1) % alignment;
		else
				alignment = (alignment-1) & -(unsigned)sizeof(struct PoolBuf);
		alignment += sizeof(struct PoolBuf);
		/* Then, figure out a chunk size that will fit */
		t = pool->chunksize;
		pgpAssert(t);
		while (len + alignment > t)
				t *= 2;
		while ((p = (char *)pgpMemAlloc(t)) == NULL) {
				/* If that didn't work, try purging or smaller allocations */
				if (!pool->purge || !pool->purge(pool->purgearg)) {
						if (len + alignment == t)
								return NULL;
						t /= 2;
						if (t < len+alignment)
								t = len+alignment;
				}
		}

		/* Update the various pointers. */
		pool->totalsize += t;
		((struct PoolBuf *)p)->next = pool->head;
		((struct PoolBuf *)p)->size = t;
		pool->head = (struct PoolBuf *)p;
		pool->freespace = t - len - alignment;
		p += alignment;
		pool->freeptr = p + len;

		return p;
}

#ifdef DEADCODE
/*
 * Store a string in the table, returning a pointer to the string.
 */
char const *
memPoolStore(struct MemPool *pool, char const *str)
{
		unsigned len = strlen(str) + 1;
		char *p;

		p = memPoolAlloc(pool, len, 1);
		if (p)
				memcpy(p, str, len);

		return p;
}
#endif