2 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
3 * Copyright (c) 1991-1994 by Xerox Corporation. All rights reserved.
5 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
6 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
8 * Permission is hereby granted to use or copy this program
9 * for any purpose, provided the above notices are retained on all copies.
10 * Permission to modify the code and to distribute modified code is granted,
11 * provided the above notices are retained, and a notice that the code was
12 * modified is included with the above copyright notice.
14 /* Boehm, July 11, 1995 11:54 am PDT */
17 typedef struct hblkhdr hdr
;
19 # if CPP_WORDSZ != 32 && CPP_WORDSZ < 36
20 --> Get a real machine
.
24 * The 2 level tree data structure that is used to find block headers.
25 * If there are more than 32 bits in a pointer, the top level is a hash
28 * This defines HDR, GET_HDR, and SET_HDR, the main macros used to
29 * retrieve and set object headers.
31 * Since 5.0 alpha 5, we can also take advantage of a header lookup
32 * cache. This is a locally declared direct mapped cache, used inside
33 * the marker. The HC_GET_HDR macro uses and maintains this
34 * cache. Assuming we get reasonable hit rates, this shaves a few
35 * memory references from each pointer validation.
42 /* Define appropriate out-degrees for each of the two tree levels */
44 # define LOG_BOTTOM_SZ 11
45 /* Keep top index size reasonable with smaller blocks. */
47 # define LOG_BOTTOM_SZ 10
50 # define LOG_TOP_SZ (WORDSZ - LOG_BOTTOM_SZ - LOG_HBLKSIZE)
52 # define LOG_TOP_SZ 11
54 # define TOP_SZ (1 << LOG_TOP_SZ)
55 # define BOTTOM_SZ (1 << LOG_BOTTOM_SZ)
58 # define USE_HDR_CACHE
61 /* #define COUNT_HDR_CACHE_HITS */
63 extern hdr
* GC_invalid_header
; /* header for an imaginary block */
64 /* containing no objects. */
67 /* Check whether p and corresponding hhdr point to long or invalid */
68 /* object. If so, advance hhdr to */
69 /* beginning of block, or set hhdr to GC_invalid_header. */
70 #define ADVANCE(p, hhdr, source) \
72 hdr * new_hdr = GC_invalid_header; \
73 p = GC_FIND_START(p, hhdr, &new_hdr, (word)source); \
79 # ifdef COUNT_HDR_CACHE_HITS
80 extern word GC_hdr_cache_hits
;
81 extern word GC_hdr_cache_misses
;
82 # define HC_HIT() ++GC_hdr_cache_hits
83 # define HC_MISS() ++GC_hdr_cache_misses
90 word block_addr
; /* right shifted by LOG_HBLKSIZE */
94 # define HDR_CACHE_SIZE 8 /* power of 2 */
96 # define DECLARE_HDR_CACHE \
97 hdr_cache_entry hdr_cache[HDR_CACHE_SIZE]
99 # define INIT_HDR_CACHE BZERO(hdr_cache, sizeof(hdr_cache));
101 # define HCE(h) hdr_cache + (((word)(h) >> LOG_HBLKSIZE) & (HDR_CACHE_SIZE-1))
103 # define HCE_VALID_FOR(hce,h) ((hce) -> block_addr == \
104 ((word)(h) >> LOG_HBLKSIZE))
106 # define HCE_HDR(h) ((hce) -> hce_hdr)
109 /* Analogous to GET_HDR, except that in the case of large objects, it */
110 /* Returns the header for the object beginning, and updates p. */
111 /* Returns &GC_bad_header instead of 0. All of this saves a branch */
112 /* in the fast path. */
113 # define HC_GET_HDR(p, hhdr, source) \
115 hdr_cache_entry * hce = HCE(p); \
116 if (HCE_VALID_FOR(hce, p)) { \
118 hhdr = hce -> hce_hdr; \
122 if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \
123 ADVANCE(p, hhdr, source); \
125 hce -> block_addr = (word)(p) >> LOG_HBLKSIZE; \
126 hce -> hce_hdr = hhdr; \
131 #else /* !USE_HDR_CACHE */
133 # define DECLARE_HDR_CACHE
135 # define INIT_HDR_CACHE
137 # define HC_GET_HDR(p, hhdr, source) \
140 if (IS_FORWARDING_ADDR_OR_NIL(hhdr)) { \
141 ADVANCE(p, hhdr, source); \
147 hdr
* index
[BOTTOM_SZ
];
149 * The bottom level index contains one of three kinds of values:
150 * 0 means we're not responsible for this block,
151 * or this is a block other than the first one in a free block.
152 * 1 < (long)X <= MAX_JUMP means the block starts at least
153 * X * HBLKSIZE bytes before the current address.
154 * A valid pointer points to a hdr structure. (The above can't be
155 * valid pointers due to the GET_MEM return convention.)
157 struct bi
* asc_link
; /* All indices are linked in */
158 /* ascending order... */
159 struct bi
* desc_link
; /* ... and in descending order. */
160 word key
; /* high order address bits. */
162 struct bi
* hash_link
; /* Hash chain link. */
166 /* extern bottom_index GC_all_nils; - really part of GC_arrays */
168 /* extern bottom_index * GC_top_index []; - really part of GC_arrays */
169 /* Each entry points to a bottom_index. */
170 /* On a 32 bit machine, it points to */
171 /* the index for a set of high order */
172 /* bits equal to the index. For longer */
173 /* addresses, we hash the high order */
174 /* bits to compute the index in */
175 /* GC_top_index, and each entry points */
176 /* to a hash chain. */
177 /* The last entry in each chain is */
181 # define MAX_JUMP (HBLKSIZE - 1)
183 # define HDR_FROM_BI(bi, p) \
184 ((bi)->index[((word)(p) >> LOG_HBLKSIZE) & (BOTTOM_SZ - 1)])
186 # define BI(p) (GC_top_index \
187 [(word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE)])
188 # define HDR_INNER(p) HDR_FROM_BI(BI(p),p)
190 # define HDR(p) GC_find_header((ptr_t)(p))
192 # define HDR(p) HDR_INNER(p)
194 # define GET_BI(p, bottom_indx) (bottom_indx) = BI(p)
195 # define GET_HDR(p, hhdr) (hhdr) = HDR(p)
196 # define SET_HDR(p, hhdr) HDR_INNER(p) = (hhdr)
197 # define GET_HDR_ADDR(p, ha) (ha) = &(HDR_INNER(p))
199 /* Hash function for tree top level */
200 # define TL_HASH(hi) ((hi) & (TOP_SZ - 1))
201 /* Set bottom_indx to point to the bottom index for address p */
202 # define GET_BI(p, bottom_indx) \
205 (word)(p) >> (LOG_BOTTOM_SZ + LOG_HBLKSIZE); \
206 register bottom_index * _bi = GC_top_index[TL_HASH(hi)]; \
208 while (_bi -> key != hi && _bi != GC_all_nils) \
209 _bi = _bi -> hash_link; \
210 (bottom_indx) = _bi; \
212 # define GET_HDR_ADDR(p, ha) \
214 register bottom_index * bi; \
217 (ha) = &(HDR_FROM_BI(bi, p)); \
219 # define GET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
221 # define SET_HDR(p, hhdr) { register hdr ** _ha; GET_HDR_ADDR(p, _ha); \
223 # define HDR(p) GC_find_header((ptr_t)(p))
226 /* Is the result a forwarding address to someplace closer to the */
227 /* beginning of the block or NIL? */
228 # define IS_FORWARDING_ADDR_OR_NIL(hhdr) ((unsigned long) (hhdr) <= MAX_JUMP)
230 /* Get an HBLKSIZE aligned address closer to the beginning of the block */
231 /* h. Assumes hhdr == HDR(h) and IS_FORWARDING_ADDR(hhdr). */
232 # define FORWARDED_ADDR(h, hhdr) ((struct hblk *)(h) - (unsigned long)(hhdr))
233 # endif /* GC_HEADERS_H */