1 files changed, 76 insertions, 0 deletions
diff --git a/shared/nm-std-aux/nm-std-utils.c b/shared/nm-std-aux/nm-std-utils.c
new file mode 100644
index 0000000000..f6c2bc43ff
--- /dev/null
+++ b/shared/nm-std-aux/nm-std-utils.c
@@ -0,0 +1,76 @@
+// 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;
+}