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Split 'xpalloc' into two functions

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The new function 'xpalloc_nbytes' calculates the new size without
performing the actual allocation.

* src/alloc.c (xpalloc_nbytes): New function.
(xpalloc): Use it.
This commit is contained in:
Pip Cet 2025-02-07 17:37:52 +00:00
parent 90bcde0139
commit eae38efc43
2 changed files with 48 additions and 20 deletions
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67
src/alloc.c
View file

@ -801,32 +801,25 @@ xnrealloc (void *pa, ptrdiff_t nitems, ptrdiff_t item_size)
}
/* Grow PA, which points to an array of *NITEMS items, and return the
location of the reallocated array, updating *NITEMS to reflect its
new size. The new array will contain at least NITEMS_INCR_MIN more
items, but will not contain more than NITEMS_MAX items total.
ITEM_SIZE is the size of each item, in bytes.
/* Calculate the new allocation size for xpalloc, for growing PA, which
points to an array of *NITEMS items, and return the size of the new
allocation, updating *NITEMS to reflect this new size. This new array
would contain at least NITEMS_INCR_MIN more items, but will not
contain more than NITEMS_MAX items total. ITEM_SIZE is the size of
each item, in bytes.
ITEM_SIZE and NITEMS_INCR_MIN must be positive. *NITEMS must be
nonnegative. If NITEMS_MAX is -1, it is treated as if it were
infinity.
If PA is null, then allocate a new array instead of reallocating
the old one.
If PA is null, then calculate the size of a new array.
Block interrupt input as needed. If memory exhaustion occurs, set
*NITEMS to zero if PA is null, and signal an error (i.e., do not
return).
If memory exhaustion is certain to occur, set *NITEMS to zero if PA
is null, and signal an error (i.e., do not return). */
Thus, to grow an array A without saving its old contents, do
{ xfree (A); A = NULL; A = xpalloc (NULL, &AITEMS, ...); }.
The A = NULL avoids a dangling pointer if xpalloc exhausts memory
and signals an error, and later this code is reexecuted and
attempts to free A. */
void *
xpalloc (void *pa, ptrdiff_t *nitems, ptrdiff_t nitems_incr_min,
ptrdiff_t nitems_max, ptrdiff_t item_size)
ptrdiff_t
xpalloc_nbytes (void *pa, ptrdiff_t *nitems, ptrdiff_t nitems_incr_min,
ptrdiff_t nitems_max, ptrdiff_t item_size)
{
ptrdiff_t n0 = *nitems;
eassume (0 < item_size && 0 < nitems_incr_min && 0 <= n0 && -1 <= nitems_max);
@ -864,8 +857,42 @@ xpalloc (void *pa, ptrdiff_t *nitems, ptrdiff_t nitems_incr_min,
|| (0 <= nitems_max && nitems_max < n)
|| ckd_mul (&nbytes, n, item_size)))
memory_full (SIZE_MAX);
pa = xrealloc (pa, nbytes);
*nitems = n;
return nbytes;
}
/* Grow PA, which points to an array of *NITEMS items, and return the
location of the reallocated array, updating *NITEMS to reflect its
new size. The new array will contain at least NITEMS_INCR_MIN more
items, but will not contain more than NITEMS_MAX items total.
ITEM_SIZE is the size of each item, in bytes.
ITEM_SIZE and NITEMS_INCR_MIN must be positive. *NITEMS must be
nonnegative. If NITEMS_MAX is -1, it is treated as if it were
infinity.
If PA is null, then allocate a new array instead of reallocating
the old one.
Block interrupt input as needed. If memory exhaustion occurs, set
*NITEMS to zero if PA is null, and signal an error (i.e., do not
return).
Thus, to grow an array A without saving its old contents, do
{ xfree (A); A = NULL; A = xpalloc (NULL, &AITEMS, ...); }.
The A = NULL avoids a dangling pointer if xpalloc exhausts memory
and signals an error, and later this code is reexecuted and
attempts to free A. */
void *
xpalloc (void *pa, ptrdiff_t *nitems, ptrdiff_t nitems_incr_min,
ptrdiff_t nitems_max, ptrdiff_t item_size)
{
ptrdiff_t nitems_new = *nitems;
ptrdiff_t nbytes = xpalloc_nbytes (pa, &nitems_new, nitems_incr_min,
nitems_max, item_size);
pa = xrealloc (pa, nbytes);
*nitems = nitems_new;
return pa;
}

1
src/lisp.h
View file

@ -5903,6 +5903,7 @@ extern void *xnmalloc (ptrdiff_t, ptrdiff_t)
ATTRIBUTE_MALLOC_SIZE ((1,2)) ATTRIBUTE_RETURNS_NONNULL;
extern void *xnrealloc (void *, ptrdiff_t, ptrdiff_t)
ATTRIBUTE_ALLOC_SIZE ((2,3)) ATTRIBUTE_RETURNS_NONNULL;
extern ptrdiff_t xpalloc_nbytes (void *, ptrdiff_t *, ptrdiff_t, ptrdiff_t, ptrdiff_t);
extern void *xpalloc (void *, ptrdiff_t *, ptrdiff_t, ptrdiff_t, ptrdiff_t)
ATTRIBUTE_RETURNS_NONNULL;