77 lines
2.2 KiB
C
77 lines
2.2 KiB
C
// SPDX-License-Identifier: LGPL-2.1+
|
|
|
|
#include "nm-default.h"
|
|
|
|
#include "nm-std-utils.h"
|
|
|
|
#include <stdint.h>
|
|
|
|
/*****************************************************************************/
|
|
|
|
size_t
|
|
nm_utils_get_next_realloc_size (bool true_realloc, size_t requested)
|
|
{
|
|
size_t n, x;
|
|
|
|
/* https://doc.qt.io/qt-5/containers.html#growth-strategies */
|
|
|
|
if (requested <= 40) {
|
|
/* small allocations. Increase in small steps of 8 bytes.
|
|
*
|
|
* We get thus sizes of 8, 16, 32, 40. */
|
|
if (requested <= 8)
|
|
return 8;
|
|
if (requested <= 16)
|
|
return 16;
|
|
if (requested <= 32)
|
|
return 32;
|
|
|
|
/* The return values for < 104 are essentially hard-coded, and the choice here is
|
|
* made without very strong reasons.
|
|
*
|
|
* We want to stay 24 bytes below the power-of-two border 64. Hence, return 40 here.
|
|
* However, the next step then is already 104 (128 - 24). It's a larger gap than in
|
|
* the steps before.
|
|
*
|
|
* It's not clear whether some of the steps should be adjusted (or how exactly). */
|
|
return 40;
|
|
}
|
|
|
|
if ( requested <= 0x2000u - 24u
|
|
|| NM_UNLIKELY (!true_realloc)) {
|
|
/* mid sized allocations. Return next power of two, minus 24 bytes extra space
|
|
* at the beginning.
|
|
* That means, we double the size as we grow.
|
|
*
|
|
* With !true_realloc, it means that the caller does not intend to call
|
|
* realloc() but instead clone the buffer. This is for example the case, when we
|
|
* want to nm_explicit_bzero() the old buffer. In that case we really want to grow
|
|
* the buffer exponentially every time and not increment in page sizes of 4K (below).
|
|
*
|
|
* We get thus sizes of 104, 232, 488, 1000, 2024, 4072, 8168... */
|
|
|
|
if (NM_UNLIKELY (requested > SIZE_MAX / 2u - 24u))
|
|
return SIZE_MAX;
|
|
|
|
x = requested + 24u;
|
|
n = 128u;
|
|
while (n < x) {
|
|
n <<= 1;
|
|
nm_assert (n > 128u);
|
|
}
|
|
|
|
nm_assert (n > 24u && n - 24u >= requested);
|
|
return n - 24u;
|
|
}
|
|
|
|
if (NM_UNLIKELY (requested > SIZE_MAX - 0x1000u - 24u))
|
|
return SIZE_MAX;
|
|
|
|
/* For large allocations (with !true_realloc) we allocate memory in chunks of
|
|
* 4K (- 24 bytes extra), assuming that the memory gets mmapped and thus
|
|
* realloc() is efficient by just reordering pages. */
|
|
n = ((requested + (0x0FFFu + 24u)) & ~((size_t) 0x0FFFu)) - 24u;
|
|
nm_assert (n >= requested);
|
|
return n;
|
|
}
|