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/*
 * tclAlloc.c --
 *
 *	This is a very fast storage allocator.  It allocates blocks of a
 *	small number of different sizes, and keeps free lists of each size.
 *	Blocks that don't exactly fit are passed up to the next larger size.
 *	Blocks over a certain size are directly allocated from the system.
 *
 * Copyright (c) 1983 Regents of the University of California.
 * Copyright (c) 1996-1997 Sun Microsystems, Inc.
 * Copyright (c) 1998-1999 by Scriptics Corporation.
 *
 * Portions contributed by Chris Kingsley, Jack Jansen and Ray Johnson.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclAlloc.c,v 1.16 2002/04/23 17:03:34 hobbs Exp $
 */

/*
 * Windows and Unix use an alternative allocator when building with threads
 * that has significantly reduced lock contention.
 */

#if !defined(TCL_THREADS) || !defined(USE_THREAD_ALLOC)

#include "tclInt.h"
#include "tclPort.h"

#if USE_TCLALLOC

#ifdef TCL_DEBUG
#   define DEBUG
/* #define MSTATS */
#   define RCHECK
#endif

/*
 * We should really make use of AC_CHECK_TYPE(caddr_t)
 * here, but it can wait until Tcl uses config.h properly.
 */
#if defined(MAC_TCL) || defined(_MSC_VER) || defined(__MINGW32__) || defined(__BORLANDC__)
typedef unsigned long caddr_t;
#endif

/*
 * The overhead on a block is at least 8 bytes.  When free, this space
 * contains a pointer to the next free block, and the bottom two bits must
 * be zero.  When in use, the first byte is set to MAGIC, and the second
 * byte is the size index.  The remaining bytes are for alignment.
 * If range checking is enabled then a second word holds the size of the
 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC).
 * The order of elements is critical: ov_magic must overlay the low order
 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern.
 */

union overhead {
    union overhead *ov_next;	/* when free */
    unsigned char ov_padding[8]; /* Ensure the structure is 8-byte aligned. */
    struct {
	unsigned char	ovu_magic0;	/* magic number */
	unsigned char	ovu_index;	/* bucket # */
	unsigned char	ovu_unused;	/* unused */
	unsigned char	ovu_magic1;	/* other magic number */
#ifdef RCHECK
	unsigned short	ovu_rmagic;	/* range magic number */
	unsigned long	ovu_size;	/* actual block size */
	unsigned short  ovu_unused2;    /* padding to 8-byte align */
#endif
    } ovu;
#define ov_magic0	ovu.ovu_magic0
#define ov_magic1	ovu.ovu_magic1
#define ov_index	ovu.ovu_index
#define ov_rmagic	ovu.ovu_rmagic
#define ov_size		ovu.ovu_size
};


#define MAGIC		0xef		/* magic # on accounting info */
#define RMAGIC		0x5555		/* magic # on range info */

#ifdef RCHECK
#define	RSLOP		sizeof (unsigned short)
#else
#define	RSLOP		0
#endif

#define OVERHEAD (sizeof(union overhead) + RSLOP)

/*
 * nextf[i] is the pointer to the next free block of size 2^(i+3).  The
 * smallest allocatable block is 8 bytes.  The overhead information
 * precedes the data area returned to the user.
 */

#define NBUCKETS	13
#define MAXMALLOC	(1<<(NBUCKETS+2))
static	union overhead *nextf[NBUCKETS];

/*
 * The following structure is used to keep track of all system memory
 * currently owned by Tcl.  When finalizing, all this memory will
 * be returned to the system.
 */

struct block {
    struct block *nextPtr;	/* Linked list. */
    struct block *prevPtr;	/* Linked list for big blocks, ensures 8-byte
				 * alignment for suballocated blocks. */
};

static struct block *blockList;		/* Tracks the suballocated blocks. */
static struct block bigBlocks = {	/* Big blocks aren't suballocated. */