From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001
From: Vladimir Azarov <avm@intermediate-node.net>
Date: Tue, 1 Oct 2024 15:47:05 +0200
Subject: Initial version

---
 src/malloc/mallocng/realloc.c | 51 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 src/malloc/mallocng/realloc.c

(limited to 'src/malloc/mallocng/realloc.c')

diff --git a/src/malloc/mallocng/realloc.c b/src/malloc/mallocng/realloc.c
new file mode 100644
index 0000000..18769f4
--- /dev/null
+++ b/src/malloc/mallocng/realloc.c
@@ -0,0 +1,51 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <string.h>
+#include "meta.h"
+
+void *realloc(void *p, size_t n)
+{
+	if (!p) return malloc(n);
+	if (size_overflows(n)) return 0;
+
+	struct meta *g = get_meta(p);
+	int idx = get_slot_index(p);
+	size_t stride = get_stride(g);
+	unsigned char *start = g->mem->storage + stride*idx;
+	unsigned char *end = start + stride - IB;
+	size_t old_size = get_nominal_size(p, end);
+	size_t avail_size = end-(unsigned char *)p;
+	void *new;
+
+	// only resize in-place if size class matches
+	if (n <= avail_size && n<MMAP_THRESHOLD
+	    && size_to_class(n)+1 >= g->sizeclass) {
+		set_size(p, end, n);
+		return p;
+	}
+
+	// use mremap if old and new size are both mmap-worthy
+	if (g->sizeclass>=48 && n>=MMAP_THRESHOLD) {
+		assert(g->sizeclass==63);
+		size_t base = (unsigned char *)p-start;
+		size_t needed = (n + base + UNIT + IB + 4095) & -4096;
+		new = g->maplen*4096UL == needed ? g->mem :
+			mremap(g->mem, g->maplen*4096UL, needed, MREMAP_MAYMOVE);
+		if (new!=MAP_FAILED) {
+			g->mem = new;
+			g->maplen = needed/4096;
+			p = g->mem->storage + base;
+			end = g->mem->storage + (needed - UNIT) - IB;
+			*end = 0;
+			set_size(p, end, n);
+			return p;
+		}
+	}
+
+	new = malloc(n);
+	if (!new) return 0;
+	memcpy(new, p, n < old_size ? n : old_size);
+	free(p);
+	return new;
+}
-- 
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