Fix comment about inv_sz computation in setup_header

(a cherry-pick of commit e55f4632 from 'master')

* allchblk.c [MARK_BIT_PER_OBJ] (setup_header): Fix comment
(sz*inv_sz>=2**32).
* allchblk.c [MARK_BIT_PER_OBJ && INV_SZ_COMPUTATION_CHECK]
(setup_header): Add assertion to check the computation of inv_sz.

diff --git a/allchblk.c b/allchblk.c
index 8dc730d0544a4c6565ea1247bf02a5d357a0684b..461d92865ad2810127790b5d5124a31db44bcfa5 100644 (file)
--- a/allchblk.c
+++ b/allchblk.c
@@ -243,7 +243,7 @@ static GC_bool setup_header(hdr * hhdr, struct hblk *block, size_t byte_sz,
 
 #   ifdef MARK_BIT_PER_OBJ
      /* Set hb_inv_sz as portably as possible.                          */
-     /* We set it to the smallest value such that sz * inv_sz > 2**32    */
+     /* We set it to the smallest value such that sz * inv_sz >= 2**32  */
      /* This may be more precision than necessary.                      */
       if (byte_sz > MAXOBJBYTES) {
          hhdr -> hb_inv_sz = LARGE_INV_SZ;
@@ -258,6 +258,9 @@ static GC_bool setup_header(hdr * hhdr, struct hblk *block, size_t byte_sz,
           inv_sz = ((unsigned)1 << 31)/byte_sz;
           inv_sz *= 2;
           while (inv_sz*byte_sz > byte_sz) ++inv_sz;
+#       endif
+#       ifdef INV_SZ_COMPUTATION_CHECK
+          GC_ASSERT(((1ULL << 32) + byte_sz - 1) / byte_sz == inv_sz);
 #       endif
         hhdr -> hb_inv_sz = inv_sz;
       }