using malloc implementation types/macros/idioms for memalign

the generated code should be mostly unchanged, except for explicit use
of C_INUSE in place of copying the low bits from existing chunk
headers/footers.

these changes also remove mild UB due to dubious arithmetic on
pointers into imaginary size_t[] arrays.

diff --git a/src/malloc/memalign.c b/src/malloc/memalign.c
index 8fb2002ca87ce0ad6a577bd3977691eefa50f497..9c420229be823007ac22bebaf3dea8d0082149ce 100644 (file)
--- a/src/malloc/memalign.c
+++ b/src/malloc/memalign.c
@@ -2,49 +2,51 @@
 #include <stdint.h>
 #include <errno.h>
 #include "libc.h"
+#include "malloc_impl.h"
 
 void *__memalign(size_t align, size_t len)
 {
-       unsigned char *mem, *new, *end;
-       size_t header, footer;
+       unsigned char *mem, *new;
 
        if ((align & -align) != align) {
                errno = EINVAL;
-               return NULL;
+               return 0;
        }
 
        if (len > SIZE_MAX - align) {
                errno = ENOMEM;
-               return NULL;
+               return 0;
        }
 
-       if (align <= 4*sizeof(size_t)) {
-               if (!(mem = malloc(len)))
-                       return NULL;
-               return mem;
-       }
+       if (align <= SIZE_ALIGN)
+               return malloc(len);
 
        if (!(mem = malloc(len + align-1)))
-               return NULL;
+               return 0;
 
        new = (void *)((uintptr_t)mem + align-1 & -align);
        if (new == mem) return mem;
 
-       header = ((size_t *)mem)[-1];
+       struct chunk *c = MEM_TO_CHUNK(mem);
+       struct chunk *n = MEM_TO_CHUNK(new);
 
-       if (!(header & 7)) {
-               ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
-               ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
+       if (IS_MMAPPED(c)) {
+               /* Apply difference between aligned and original
+                * address to the "extra" field of mmapped chunk. */
+               n->psize = c->psize + (new-mem);
+               n->csize = c->csize - (new-mem);
                return new;
        }
 
-       end = mem + (header & -8);
-       footer = ((size_t *)end)[-2];
+       struct chunk *t = NEXT_CHUNK(c);
 
-       ((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;
+       /* Split the allocated chunk into two chunks. The aligned part
+        * that will be used has the size in its footer reduced by the
+        * difference between the aligned and original addresses, and
+        * the resulting size copied to its header. A new header and
+        * footer are written for the split-off part to be freed. */
+       n->psize = c->csize = C_INUSE | (new-mem);
+       n->csize = t->psize -= new-mem;
 
        free(mem);
        return new;