optimization for chunk canaries

[Otto Moerbeek]

Hi,

avoid recomping the offset by storing it in the chunk info, ok?

        -Otto

Index: stdlib/malloc.c
===================================================================
RCS file: /cvs/src/lib/libc/stdlib/malloc.c,v
retrieving revision 1.199
diff -u -p -r1.199 malloc.c
--- stdlib/malloc.c     7 Oct 2016 05:55:37 -0000       1.199
+++ stdlib/malloc.c     8 Oct 2016 16:38:07 -0000
@@ -165,6 +165,7 @@ struct chunk_info {
        u_short shift;                  /* how far to shift for this size */
        u_short free;                   /* how many free chunks */
        u_short total;                  /* how many chunks */
+       u_short offset;                 /* requested size table offset */
                                        /* which chunks are free */
        u_short bits[1];
 };
@@ -916,6 +917,7 @@ omalloc_make_chunks(struct dir_info *d, 
                bp->size = 1U << bits;
                bp->shift = bits;
                bp->total = bp->free = MALLOC_PAGESIZE >> bits;
+               bp->offset = howmany(bp->total, MALLOC_BITS);
                bp->page = pp;
        }
 
@@ -1025,7 +1027,7 @@ malloc_bytes(struct dir_info *d, size_t 
        k += (lp - bp->bits) * MALLOC_BITS;
        
        if (mopts.chunk_canaries)
-               bp->bits[howmany(bp->total, MALLOC_BITS) + k] = argsize;
+               bp->bits[bp->offset + k] = argsize;
 
        k <<= bp->shift;
 
@@ -1056,8 +1058,7 @@ find_chunknum(struct dir_info *d, struct
        /* Find the chunk number on the page */
        chunknum = ((uintptr_t)ptr & MALLOC_PAGEMASK) >> info->shift;
        if (check && mopts.chunk_canaries && info->size > 0) {
-               size_t sz = info->bits[howmany(info->total, MALLOC_BITS) +
-                   chunknum];
+               size_t sz = info->bits[info->offset + chunknum];
                size_t check_sz = info->size - sz;
                u_char *p, *q;
 
@@ -1280,7 +1281,8 @@ malloc(size_t size)
 /*DEF_STRONG(malloc);*/
 
 static void
-validate_junk(struct dir_info *pool, void *p) {
+validate_junk(struct dir_info *pool, void *p)
+{
        struct region_info *r;
        size_t byte, sz;