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/*

 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers

 * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.

 *

 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED

 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.

 *

 * Permission is hereby granted to use or copy this program

 * for any purpose,  provided the above notices are retained on all copies.

 * Permission to modify the code and to distribute modified code is granted,

 * provided the above notices are retained, and a notice that the code was

 * modified is included with the above copyright notice.

 */

/* Boehm, July 11, 1995 11:54 am PDT */

# ifndef GC_HEADERS_H

# define GC_HEADERS_H

typedef struct hblkhdr hdr;

# if CPP_WORDSZ != 32 && CPP_WORDSZ < 36

        --> Get a real machine.

# endif

/*

 * The 2 level tree data structure that is used to find block headers.

 * If there are more than 32 bits in a pointer, the top level is a hash

 * table.

 *

 * This defines HDR, GET_HDR, and SET_HDR, the main macros used to

 * retrieve and set object headers.

 *

 * Since 5.0 alpha 5, we can also take advantage of a header lookup

 * cache.  This is a locally declared direct mapped cache, used inside

 * the marker.  The HC_GET_HDR macro uses and maintains this

 * cache.  Assuming we get reasonable hit rates, this shaves a few

 * memory references from each pointer validation.

 */

# if CPP_WORDSZ > 32

#   define HASH_TL

# endif

/* Define appropriate out-degrees for each of the two tree levels       */

# ifdef SMALL_CONFIG

#   define LOG_BOTTOM_SZ 11

        /* Keep top index size reasonable with smaller blocks. */

# else

#   define LOG_BOTTOM_SZ 10

# endif

# ifndef HASH_TL

#   define LOG_TOP_SZ (WORDSZ - LOG_BOTTOM_SZ - LOG_HBLKSIZE)

# else

#   define LOG_TOP_SZ 11

# endif

# define TOP_SZ (1 << LOG_TOP_SZ)

# define BOTTOM_SZ (1 << LOG_BOTTOM_SZ)

#ifndef SMALL_CONFIG

# define USE_HDR_CACHE

#endif

/* #define COUNT_HDR_CACHE_HITS  */

extern hdr * GC_invalid_header; /* header for an imaginary block        */

                                /* containing no objects.               */

/* Check whether p and corresponding hhdr point to long or invalid      */

/* object.  If so, advance hhdr to                                      */

/* beginning of block, or set hhdr to GC_invalid_header.                */

#define ADVANCE(p, hhdr, source) \

            { \

              hdr * new_hdr = GC_invalid_header; \

              p = GC_find_start(p, hhdr, &new_hdr); \

              hhdr = new_hdr; \

            }

#ifdef USE_HDR_CACHE

# ifdef COUNT_HDR_CACHE_HITS

    extern word GC_hdr_cache_hits;

    extern word GC_hdr_cache_misses;

#   define HC_HIT() ++GC_hdr_cache_hits

#   define HC_MISS() ++GC_hdr_cache_misses

# else

#   define HC_HIT()

#   define HC_MISS()

# endif

  typedef struct hce {

    word block_addr;    /* right shifted by LOG_HBLKSIZE */

    hdr * hce_hdr;

  } hdr_cache_entry;

# define HDR_CACHE_SIZE 8  /* power of 2 */

# define DECLARE_HDR_CACHE \

        hdr_cache_entry hdr_cache[HDR_CACHE_SIZE]

# define INIT_HDR_CACHE BZERO(hdr_cache, sizeof(hdr_cache));

# define HCE(h) hdr_cache + (((word)(h) >> LOG_HBLKSIZE) & (HDR_CACHE_SIZE-1))

# define HCE_VALID_FOR(hce,h) ((hce) -> block_addr == \

                                ((word)(h) >> LOG_HBLKSIZE))

# define HCE_HDR(h) ((hce) -> hce_hdr)

/* Analogous to GET_HDR, except that in the case of large objects, it   */

/* Returns the header for the object beginning, and updates p.          */

/* Returns GC_invalid_header instead of 0.  All of this saves a branch  */

/* in the fast path.                                                    */

# define HC_GET_HDR(p, hhdr, source) \

        { \

          hdr_cache_entry * hce = HCE(p); \

          if (HCE_VALID_FOR(hce, p)) { \

            HC_HIT(); \

            hhdr = hce -> hce_hdr; \

          } else { \

            HC_MISS(); \

            GET_HDR(p, hhdr); \

            if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \

              ADVANCE(p, hhdr, source); \

            } else { \

              hce -> block_addr = (word)(p) >> LOG_HBLKSIZE; \

              hce -> hce_hdr = hhdr; \

            } \

          } \

        }

#else /* !USE_HDR_CACHE */

# define DECLARE_HDR_CACHE

# define INIT_HDR_CACHE

# define HC_GET_HDR(p, hhdr, source) \

        { \

          GET_HDR(p, hhdr); \

          if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \

            ADVANCE(p, hhdr, source); \

          } \

        }

#endif

typedef struct bi {

    hdr * index[BOTTOM_SZ];

        /*

         * The bottom level index contains one of three kinds of values:

         * 0 means we're not responsible for this block,

         *   or this is a block other than the first one in a free block.

         * 1 < (long)X <= MAX_JUMP means the block starts at least

         *        X * HBLKSIZE bytes before the current address.

         * A valid pointer points to a hdr structure. (The above can't be

         * valid pointers due to the GET_MEM return convention.)

         */

    struct bi * asc_link;       /* All indices are linked in    */

                                /* ascending order...           */

    struct bi * desc_link;      /* ... and in descending order. */

    word key;                   /* high order address bits.     */

# ifdef HASH_TL

    struct bi * hash_link;      /* Hash chain link.             */

# endif

} bottom_index;

/* extern bottom_index GC_all_nils; - really part of GC_arrays */

/* extern bottom_index * GC_top_index []; - really part of GC_arrays */

                                /* Each entry points to a bottom_index. */

                                /* On a 32 bit machine, it points to    */

                                /* the index for a set of high order    */

                                /* bits equal to the index.  For longer */

                                /* addresses, we hash the high order    */

                                /* bits to compute the index in         */

                                /* GC_top_index, and each entry points  */

                                /* to a hash chain.                     */

                                /* The last entry in each chain is      */

                                /* GC_all_nils.                         */

# define MAX_JUMP (HBLKSIZE - 1)

# define HDR_FROM_BI(bi, p) \

                ((bi)->index[((word)(p) >> LOG_HBLKSIZE) & (BOTTOM_SZ - 1)])

# ifndef HASH_TL

#   define BI(p) (GC_top_index \

                [(word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE)])

#   define HDR_INNER(p) HDR_FROM_BI(BI(p),p)

#   ifdef SMALL_CONFIG

#       define HDR(p) GC_find_header((ptr_t)(p))

#   else

#       define HDR(p) HDR_INNER(p)

#   endif

#   define GET_BI(p, bottom_indx) (bottom_indx) = BI(p)

#   define GET_HDR(p, hhdr) (hhdr) = HDR(p)

#   define SET_HDR(p, hhdr) HDR_INNER(p) = (hhdr)

#   define GET_HDR_ADDR(p, ha) (ha) = &(HDR_INNER(p))

# else /* hash */

/*  Hash function for tree top level */

#   define TL_HASH(hi) ((hi) & (TOP_SZ - 1))

/*  Set bottom_indx to point to the bottom index for address p */

#   define GET_BI(p, bottom_indx) \

        { \

            register word hi = \

                (word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \

            register bottom_index * _bi = GC_top_index[TL_HASH(hi)]; \

            \

            while (_bi -> key != hi && _bi != GC_all_nils) \

                _bi = _bi -> hash_link; \

            (bottom_indx) = _bi; \

        }

#   define GET_HDR_ADDR(p, ha) \

        { \

            register bottom_index * bi; \

            \

            GET_BI(p, bi);      \

            (ha) = &(HDR_FROM_BI(bi, p)); \

        }

#   define GET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \

                              (hhdr) = *_ha; }

#   define SET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \

                              *_ha = (hhdr); }

#   define HDR(p) GC_find_header((ptr_t)(p))

# endif

/* Is the result a forwarding address to someplace closer to the        */

/* beginning of the block or NIL?                                       */

# define IS_FORWARDING_ADDR_OR_NIL(hhdr) ((unsigned long) (hhdr) <= MAX_JUMP)

/* Get an HBLKSIZE aligned address closer to the beginning of the block */

/* h.  Assumes hhdr == HDR(h) and IS_FORWARDING_ADDR(hhdr).             */

# define FORWARDED_ADDR(h, hhdr) ((struct hblk *)(h) - (unsigned long)(hhdr))

# endif /*  GC_HEADERS_H */