diff options
author | Calvin Wan <calvinwan@google.com> | 2023-07-05 20:09:24 +0300 |
---|---|---|
committer | Junio C Hamano <gitster@pobox.com> | 2023-07-05 21:42:31 +0300 |
commit | 91c080dff511b7a81f91d1cc79589b49e16a2b7a (patch) | |
tree | 5730d26a094848ca2f652c507ce54519b981ef84 /git-compat-util.h | |
parent | da9502ff4dc495471a1a080dc297cd6e4628c10c (diff) |
git-compat-util: move alloc macros to git-compat-util.h
alloc_nr, ALLOC_GROW, and ALLOC_GROW_BY are commonly used macros for
dynamic array allocation. Moving these macros to git-compat-util.h with
the other alloc macros focuses alloc.[ch] to allocation for Git objects
and additionally allows us to remove inclusions to alloc.h from files
that solely used the above macros.
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'git-compat-util.h')
-rw-r--r-- | git-compat-util.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/git-compat-util.h b/git-compat-util.h index 9d3c21acbb..0d0b42b253 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -1134,6 +1134,81 @@ static inline void move_array(void *dst, const void *src, size_t n, size_t size) #define FLEXPTR_ALLOC_STR(x, ptrname, str) \ FLEXPTR_ALLOC_MEM((x), ptrname, (str), strlen(str)) +#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) + static inline char *xstrdup_or_null(const char *str) { return str ? xstrdup(str) : NULL; |