diff options
Diffstat (limited to 'alloc.h')
| -rw-r--r-- | alloc.h | 75 |
1 files changed, 75 insertions, 0 deletions
@@ -17,4 +17,79 @@ void *alloc_object_node(struct repository *r); struct alloc_state *allocate_alloc_state(void); void clear_alloc_state(struct alloc_state *s); +#define alloc_nr(x) (((x)+16)*3/2) + +/** + * Dynamically growing an array using realloc() is error prone and boring. + * + * Define your array with: + * + * - a pointer (`item`) that points at the array, initialized to `NULL` + * (although please name the variable based on its contents, not on its + * type); + * + * - an integer variable (`alloc`) that keeps track of how big the current + * allocation is, initialized to `0`; + * + * - another integer variable (`nr`) to keep track of how many elements the + * array currently has, initialized to `0`. + * + * Then before adding `n`th element to the item, call `ALLOC_GROW(item, n, + * alloc)`. This ensures that the array can hold at least `n` elements by + * calling `realloc(3)` and adjusting `alloc` variable. + * + * ------------ + * sometype *item; + * size_t nr; + * size_t alloc + * + * for (i = 0; i < nr; i++) + * if (we like item[i] already) + * return; + * + * // we did not like any existing one, so add one + * ALLOC_GROW(item, nr + 1, alloc); + * item[nr++] = value you like; + * ------------ + * + * You are responsible for updating the `nr` variable. + * + * If you need to specify the number of elements to allocate explicitly + * then use the macro `REALLOC_ARRAY(item, alloc)` instead of `ALLOC_GROW`. + * + * Consider using ALLOC_GROW_BY instead of ALLOC_GROW as it has some + * added niceties. + * + * DO NOT USE any expression with side-effect for 'x', 'nr', or 'alloc'. + */ +#define ALLOC_GROW(x, nr, alloc) \ + do { \ + if ((nr) > alloc) { \ + if (alloc_nr(alloc) < (nr)) \ + alloc = (nr); \ + else \ + alloc = alloc_nr(alloc); \ + REALLOC_ARRAY(x, alloc); \ + } \ + } while (0) + +/* + * Similar to ALLOC_GROW but handles updating of the nr value and + * zeroing the bytes of the newly-grown array elements. + * + * DO NOT USE any expression with side-effect for any of the + * arguments. + */ +#define ALLOC_GROW_BY(x, nr, increase, alloc) \ + do { \ + if (increase) { \ + size_t new_nr = nr + (increase); \ + if (new_nr < nr) \ + BUG("negative growth in ALLOC_GROW_BY"); \ + ALLOC_GROW(x, new_nr, alloc); \ + memset((x) + nr, 0, sizeof(*(x)) * (increase)); \ + nr = new_nr; \ + } \ + } while (0) + #endif |