implement "low hanging fruit" from C11

[musl] / src / malloc / aligned_alloc.c

diff --git a/src/malloc/aligned_alloc.c b/src/malloc/aligned_alloc.c
new file mode 100644 (file)
index 0000000..d623420
--- /dev/null
+++ b/src/malloc/aligned_alloc.c
@@ -0,0 +1,51 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <errno.h>
+
+/* 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 *aligned_alloc(size_t align, size_t len)
+{
+       unsigned char *mem, *new, *end;
+       size_t header, footer;
+
+       if ((align & -align & -sizeof(void *)) != 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];
+       end = mem + (header & -8);
+       footer = ((size_t *)end)[-2];
+       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;
+       }
+
+       ((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;
+}