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[git.git] / commit-slab.h
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1 #ifndef COMMIT_SLAB_H
2 #define COMMIT_SLAB_H
4 /*
5 * define_commit_slab(slabname, elemtype) creates boilerplate code to define
6 * a new struct (struct slabname) that is used to associate a piece of data
7 * of elemtype to commits, and a few functions to use that struct.
9 * After including this header file, using:
11 * define_commit_slab(indegree, int);
13 * will let you call the following functions:
15 * - int *indegree_at(struct indegree *, struct commit *);
17 * This function locates the data associated with the given commit in
18 * the indegree slab, and returns the pointer to it. The location to
19 * store the data is allocated as necessary.
21 * - int *indegree_peek(struct indegree *, struct commit *);
23 * This function is similar to indegree_at(), but it will return NULL
24 * until a call to indegree_at() was made for the commit.
26 * - void init_indegree(struct indegree *);
27 * void init_indegree_with_stride(struct indegree *, int);
29 * Initializes the indegree slab that associates an array of integers
30 * to each commit. 'stride' specifies how big each array is. The slab
31 * that is initialized by the variant without "_with_stride" associates
32 * each commit with an array of one integer.
34 * - void clear_indegree(struct indegree *);
36 * Empties the slab. The slab can be reused with the same stride
37 * without calling init_indegree() again or can be reconfigured to a
38 * different stride by calling init_indegree_with_stride().
40 * Call this function before the slab falls out of scope to avoid
41 * leaking memory.
44 /* allocate ~512kB at once, allowing for malloc overhead */
45 #ifndef COMMIT_SLAB_SIZE
46 #define COMMIT_SLAB_SIZE (512*1024-32)
47 #endif
49 #define MAYBE_UNUSED __attribute__((__unused__))
51 #define define_commit_slab(slabname, elemtype) \
53 struct slabname { \
54 unsigned slab_size; \
55 unsigned stride; \
56 unsigned slab_count; \
57 elemtype **slab; \
58 }; \
59 static int stat_ ##slabname## realloc; \
61 static MAYBE_UNUSED void init_ ##slabname## _with_stride(struct slabname *s, \
62 unsigned stride) \
63 { \
64 unsigned int elem_size; \
65 if (!stride) \
66 stride = 1; \
67 s->stride = stride; \
68 elem_size = sizeof(elemtype) * stride; \
69 s->slab_size = COMMIT_SLAB_SIZE / elem_size; \
70 s->slab_count = 0; \
71 s->slab = NULL; \
72 } \
74 static MAYBE_UNUSED void init_ ##slabname(struct slabname *s) \
75 { \
76 init_ ##slabname## _with_stride(s, 1); \
77 } \
79 static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s) \
80 { \
81 unsigned int i; \
82 for (i = 0; i < s->slab_count; i++) \
83 free(s->slab[i]); \
84 s->slab_count = 0; \
85 FREE_AND_NULL(s->slab); \
86 } \
88 static MAYBE_UNUSED elemtype *slabname## _at_peek(struct slabname *s, \
89 const struct commit *c, \
90 int add_if_missing) \
91 { \
92 unsigned int nth_slab, nth_slot; \
94 nth_slab = c->index / s->slab_size; \
95 nth_slot = c->index % s->slab_size; \
97 if (s->slab_count <= nth_slab) { \
98 unsigned int i; \
99 if (!add_if_missing) \
100 return NULL; \
101 REALLOC_ARRAY(s->slab, nth_slab + 1); \
102 stat_ ##slabname## realloc++; \
103 for (i = s->slab_count; i <= nth_slab; i++) \
104 s->slab[i] = NULL; \
105 s->slab_count = nth_slab + 1; \
107 if (!s->slab[nth_slab]) { \
108 if (!add_if_missing) \
109 return NULL; \
110 s->slab[nth_slab] = xcalloc(s->slab_size, \
111 sizeof(**s->slab) * s->stride); \
113 return &s->slab[nth_slab][nth_slot * s->stride]; \
116 static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
117 const struct commit *c) \
119 return slabname##_at_peek(s, c, 1); \
122 static MAYBE_UNUSED elemtype *slabname## _peek(struct slabname *s, \
123 const struct commit *c) \
125 return slabname##_at_peek(s, c, 0); \
128 struct slabname
131 * Note that this redundant forward declaration is required
132 * to allow a terminating semicolon, which makes instantiations look
133 * like function declarations. I.e., the expansion of
135 * define_commit_slab(indegree, int);
137 * ends in 'struct indegree;'. This would otherwise
138 * be a syntax error according (at least) to ISO C. It's hard to
139 * catch because GCC silently parses it by default.
143 * Statically initialize a commit slab named "var". Note that this
144 * evaluates "stride" multiple times! Example:
146 * struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
149 #define COMMIT_SLAB_INIT(stride, var) { \
150 COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
151 (stride), 0, NULL \
154 #endif /* COMMIT_SLAB_H */