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authorRich Felker <dalias@aerifal.cx>2013-07-04 23:58:16 -0400
committerRich Felker <dalias@aerifal.cx>2013-07-04 23:58:16 -0400
commit6d861ac87491a207e4599c44b61d142f0a601c2d (patch)
tree2458b79e37b144f13fb5190a7bcf777d1b9b883a /src/malloc/memalign.c
parent651416182dc65d75e91cadfec65dd72f9ff07846 (diff)
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move core memalign code from aligned_alloc to __memalign
there are two motivations for this change. one is to avoid gratuitously depending on a C11 symbol for implementing a POSIX function. the other pertains to the documented semantics. C11 does not define any behavior for aligned_alloc when the length argument is not a multiple of the alignment argument. posix_memalign on the other hand places no requirements on the length argument. using __memalign as the implementation of both, rather than trying to implement one in terms of the other when their documented contracts differ, eliminates this confusion.
Diffstat (limited to 'src/malloc/memalign.c')
-rw-r--r--src/malloc/memalign.c52
1 files changed, 50 insertions, 2 deletions
diff --git a/src/malloc/memalign.c b/src/malloc/memalign.c
index a594c636..55fe68e8 100644
--- a/src/malloc/memalign.c
+++ b/src/malloc/memalign.c
@@ -1,7 +1,55 @@
#include <stdlib.h>
+#include <stdint.h>
#include <errno.h>
+#include "libc.h"
-void *memalign(size_t align, size_t len)
+/* This function should work with most dlmalloc-like chunk bookkeeping
+ * systems, but it's only guaranteed to work with the native implementation
+ * used in this library. */
+
+void *__memalign(size_t align, size_t len)
{
- return aligned_alloc(align, len);
+ unsigned char *mem, *new, *end;
+ size_t header, footer;
+
+ if ((align & -align) != align) {
+ errno = EINVAL;
+ return NULL;
+ }
+
+ if (len > SIZE_MAX - align) {
+ errno = ENOMEM;
+ return NULL;
+ }
+
+ if (align <= 4*sizeof(size_t)) {
+ if (!(mem = malloc(len)))
+ return NULL;
+ return mem;
+ }
+
+ if (!(mem = malloc(len + align-1)))
+ return NULL;
+
+ header = ((size_t *)mem)[-1];
+ new = (void *)((uintptr_t)mem + align-1 & -align);
+
+ if (!(header & 7)) {
+ ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
+ ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
+ return new;
+ }
+
+ end = mem + (header & -8);
+ footer = ((size_t *)end)[-2];
+
+ ((size_t *)mem)[-1] = header&7 | new-mem;
+ ((size_t *)new)[-2] = footer&7 | new-mem;
+ ((size_t *)new)[-1] = header&7 | end-new;
+ ((size_t *)end)[-2] = footer&7 | end-new;
+
+ if (new != mem) free(mem);
+ return new;
}
+
+weak_alias(__memalign, memalign);