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authorThomas Voss <mail@thomasvoss.com> 2024-05-09 02:09:02 +0200
committerThomas Voss <mail@thomasvoss.com> 2024-05-09 02:09:14 +0200
commit20fa17a5f2a286f44bdafff6dc4bb58e7667fe46 (patch)
tree434e02ca63f4f88a059433a4eedbd83bacc7da53
parent8f6d296a23675687177afd697cb28d195252466e (diff)
Implement arena allocation resizing
-rw-r--r--include/alloc.h9
-rw-r--r--lib/alloc/arena_alloc.c2
-rw-r--r--lib/alloc/arena_realloc.c61
-rw-r--r--lib/alloc/arena_zero.c1
4 files changed, 71 insertions, 2 deletions
diff --git a/include/alloc.h b/include/alloc.h
index 3074b27..57e7f59 100644
--- a/include/alloc.h
+++ b/include/alloc.h
@@ -11,7 +11,7 @@
struct _region {
size_t len, cap;
- void *data;
+ void *data, *last;
struct _region *next;
};
@@ -31,12 +31,17 @@ mkarena(size_t n)
return (arena){._init = n ? n : MLIB_ARENA_BLKSIZE};
}
+/* Arena allocation functions */
[[nodiscard, gnu::malloc, gnu::alloc_size(2, 3), gnu::alloc_align(4)]]
void *arena_alloc(arena *, size_t, size_t, size_t);
-
+[[nodiscard]]
+void *arena_realloc(arena *, void *, size_t, size_t, size_t, size_t);
void arena_zero(arena *);
void arena_free(arena *);
+/* Arena allocation macro wrappers */
#define arena_new(a, T, n) ((T *)arena_alloc((a), (n), sizeof(T), alignof(T)))
+#define arena_resz(a, T, p, n) \
+ ((T *)arena_realloc((a), (p), (n), sizeof(T), alignof(T)))
#endif /* !MLIB_ALLOC_H */
diff --git a/lib/alloc/arena_alloc.c b/lib/alloc/arena_alloc.c
index 814b0bb..65123d4 100644
--- a/lib/alloc/arena_alloc.c
+++ b/lib/alloc/arena_alloc.c
@@ -36,6 +36,7 @@ mkregion(size_t cap)
errno = save;
return nullptr;
}
+ r->last = r->data;
return r;
}
@@ -63,6 +64,7 @@ arena_alloc(arena *a, size_t sz, size_t n, size_t align)
if (nlen <= r->cap) {
void *ret = (char *)r->data + off;
r->len = nlen;
+ r->last = ret;
return ret;
}
}
diff --git a/lib/alloc/arena_realloc.c b/lib/alloc/arena_realloc.c
new file mode 100644
index 0000000..f13ce17
--- /dev/null
+++ b/lib/alloc/arena_realloc.c
@@ -0,0 +1,61 @@
+#include <errno.h>
+#include <stdckdint.h>
+#include <string.h>
+
+#include "alloc.h"
+#include "macros.h"
+
+void *
+arena_realloc(arena *a, void *ptr, size_t old, size_t new, size_t elemsz,
+ size_t align)
+{
+ ASSUME(a != nullptr);
+
+ if (old == new)
+ return ptr;
+
+ struct _region *cur = a->_head;
+ while (cur != nullptr) {
+ if (ptr >= cur->data && (char *)ptr < (char *)cur->data + cur->cap)
+ break;
+ cur = cur->next;
+ }
+ if (cur == nullptr)
+ cur = a->_head;
+
+ /* cur now points to the region containing ‘ptr’ */
+
+ /* If we are shrinking the buffer, then we don’t need to move our allocation
+ and can just return it directly. As a minor optimization if the
+ allocation we are shrinking is the last allocation in the current region,
+ we can decrease the region length to make space for more future
+ allocations. */
+ if (old > new) {
+ if (ptr == cur->last)
+ cur->len -= (old - new) * elemsz;
+ return ptr;
+ }
+
+ ASSUME(old < new);
+
+ /* If we need to grow the given allocation, but it was the last allocation
+ made in a region, then we first see if we can just eat more trailing free
+ space in the region to avoid a memcpy(). */
+ if (ptr == cur->last) {
+ size_t need, free = cur->cap - cur->len;
+ if (ckd_mul(&need, new - old, elemsz)) {
+ errno = EOVERFLOW;
+ return nullptr;
+ }
+ if (need <= free) {
+ cur->len += need;
+ return ptr;
+ }
+ }
+
+ /* At this point we just make a new allocation and copy the data over */
+ void *dst = arena_alloc(a, new, elemsz, align);
+ if (dst == nullptr || ptr == nullptr)
+ return nullptr;
+ return memcpy(dst, ptr, new * elemsz);
+}
diff --git a/lib/alloc/arena_zero.c b/lib/alloc/arena_zero.c
index b0e3fbe..296007e 100644
--- a/lib/alloc/arena_zero.c
+++ b/lib/alloc/arena_zero.c
@@ -9,6 +9,7 @@ arena_zero(arena *a)
struct _region *cur = a->_head;
while (cur != nullptr) {
cur->len = 0;
+ cur->last = cur->data;
cur = cur->next;
}
}