diff --git a/ChangeLog b/ChangeLog
index ea191b3bd..88fd76309 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2013-01-05  Vladimir Serbinenko  <phcoder@gmail.com>
+
+	* grub-core/fs/ntfs.c: Eliminate useless divisions in favor of shifts.
+	* grub-core/fs/ntfscomp.c: Likewise.
+	* include/grub/ntfs.h (grub_ntfs_data): Replace spc with log_spc.
+	(grub_ntfs_comp): Likewise.
+
 2013-01-05  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	* grub-core/fs/nilfs2.c (-grub_nilfs2_palloc_groups_per_desc_block):
diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index b9762b6a0..6004e1f71 100644
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -391,7 +391,7 @@ read_data (struct grub_ntfs_attr *at, char *pa, char *dest,
   grub_memset (&cc, 0, sizeof (cc));
   ctx = &cc;
   ctx->attr = at;
-  ctx->comp.spc = at->mft->data->spc;
+  ctx->comp.log_spc = at->mft->data->log_spc;
   ctx->comp.disk = at->mft->data->disk;
 
   if (pa[8] == 0)
@@ -440,11 +440,11 @@ read_data (struct grub_ntfs_attr *at, char *pa, char *dest,
 	  at->save_pos = 1;
 	}
 
-      vcn = ctx->target_vcn = (ofs >> GRUB_NTFS_COM_LOG_LEN) * (GRUB_NTFS_COM_SEC / ctx->comp.spc);
+      vcn = ctx->target_vcn = (ofs >> GRUB_NTFS_COM_LOG_LEN) * (GRUB_NTFS_COM_SEC >> ctx->comp.log_spc);
       ctx->target_vcn &= ~0xFULL;
     }
   else
-    vcn = ctx->target_vcn = grub_divmod64 (ofs >> GRUB_NTFS_BLK_SHR, ctx->comp.spc, 0);
+    vcn = ctx->target_vcn = ofs >> (GRUB_NTFS_BLK_SHR + ctx->comp.log_spc);
 
   ctx->next_vcn = u32at (pa, 0x10);
   ctx->curr_lcn = 0;
@@ -459,17 +459,17 @@ read_data (struct grub_ntfs_attr *at, char *pa, char *dest,
       grub_disk_addr_t st0, st1;
       grub_uint64_t m;
 
-      grub_divmod64 (ofs >> GRUB_NTFS_BLK_SHR, ctx->comp.spc, &m);
+      m = (ofs >> GRUB_NTFS_BLK_SHR) & ((1 << ctx->comp.log_spc) - 1);
 
       st0 =
-	(ctx->target_vcn - ctx->curr_vcn + ctx->curr_lcn) * ctx->comp.spc + m;
+	((ctx->target_vcn - ctx->curr_vcn + ctx->curr_lcn) << ctx->comp.log_spc) + m;
       st1 = st0 + 1;
       if (st1 ==
-	  (ctx->next_vcn - ctx->curr_vcn + ctx->curr_lcn) * ctx->comp.spc)
+	  (ctx->next_vcn - ctx->curr_vcn + ctx->curr_lcn) << ctx->comp.log_spc)
 	{
 	  if (grub_ntfs_read_run_list (ctx))
 	    return grub_errno;
-	  st1 = ctx->curr_lcn * ctx->comp.spc;
+	  st1 = ctx->curr_lcn << ctx->comp.log_spc;
 	}
       grub_set_unaligned32 (dest, grub_cpu_to_le32 (st0));
       grub_set_unaligned32 (dest + 4, grub_cpu_to_le32 (st1));
@@ -478,12 +478,10 @@ read_data (struct grub_ntfs_attr *at, char *pa, char *dest,
 
   if (!(ctx->flags & GRUB_NTFS_RF_COMP))
     {
-      unsigned int pow;
-
-      if (!grub_fshelp_log2blksize (ctx->comp.spc, &pow))
-	grub_fshelp_read_file (ctx->comp.disk, (grub_fshelp_node_t) ctx,
-			       read_hook, ofs, len, dest,
-			       grub_ntfs_read_block, ofs + len, pow, 0);
+      grub_fshelp_read_file (ctx->comp.disk, (grub_fshelp_node_t) ctx,
+			     read_hook, ofs, len, dest,
+			     grub_ntfs_read_block, ofs + len,
+			     ctx->comp.log_spc, 0);
       return grub_errno;
     }
 
@@ -515,11 +513,11 @@ read_attr (struct grub_ntfs_attr *at, char *dest, grub_disk_addr_t ofs,
 
       /* If compression is possible make sure that we include possible
 	 compressed block size.  */
-      if (GRUB_NTFS_COM_SEC >= at->mft->data->spc)
+      if (GRUB_NTFS_LOG_COM_SEC >= at->mft->data->log_spc)
 	vcn = ((ofs >> GRUB_NTFS_COM_LOG_LEN)
-	       * (GRUB_NTFS_COM_SEC / at->mft->data->spc)) & ~0xFULL;
+	       << (GRUB_NTFS_LOG_COM_SEC - at->mft->data->log_spc)) & ~0xFULL;
       else
-	vcn = grub_divmod64 (ofs, at->mft->data->spc << GRUB_NTFS_BLK_SHR, 0);
+	vcn = ofs >> (at->mft->data->log_spc + GRUB_NTFS_BLK_SHR);
       pa = at->attr_nxt + u16at (at->attr_nxt, 4);
       while (pa < at->attr_end)
 	{
@@ -934,6 +932,7 @@ grub_ntfs_mount (grub_disk_t disk)
 {
   struct grub_ntfs_bpb bpb;
   struct grub_ntfs_data *data = 0;
+  grub_uint32_t spc;
 
   if (!disk)
     goto fail;
@@ -955,23 +954,25 @@ grub_ntfs_mount (grub_disk_t disk)
       || (bpb.bytes_per_sector & (bpb.bytes_per_sector - 1)) != 0)
     goto fail;
 
-  data->spc = (((grub_uint32_t) bpb.sectors_per_cluster
-		* (grub_uint32_t) grub_le_to_cpu16 (bpb.bytes_per_sector))
-	       >> GRUB_NTFS_BLK_SHR);
-  if (!data->spc)
+  spc = (((grub_uint32_t) bpb.sectors_per_cluster
+	  * (grub_uint32_t) grub_le_to_cpu16 (bpb.bytes_per_sector))
+	 >> GRUB_NTFS_BLK_SHR);
+  if (spc == 0 || (spc & (spc - 1)))
     goto fail;
 
+  for (data->log_spc = 0; (1U << data->log_spc) < spc; data->log_spc++);
+
   if (bpb.clusters_per_mft > 0)
-    data->mft_size = data->spc * bpb.clusters_per_mft;
+    data->mft_size = bpb.clusters_per_mft << data->log_spc;
   else
     data->mft_size = 1 << (-bpb.clusters_per_mft - GRUB_NTFS_BLK_SHR);
 
   if (bpb.clusters_per_index > 0)
-    data->idx_size = data->spc * bpb.clusters_per_index;
+    data->idx_size = bpb.clusters_per_index << data->log_spc;
   else
     data->idx_size = 1 << (-bpb.clusters_per_index - GRUB_NTFS_BLK_SHR);
 
-  data->mft_start = grub_le_to_cpu64 (bpb.mft_lcn) * data->spc;
+  data->mft_start = grub_le_to_cpu64 (bpb.mft_lcn) << data->log_spc;
 
   if ((data->mft_size > GRUB_NTFS_MAX_MFT) || (data->idx_size > GRUB_NTFS_MAX_IDX))
     goto fail;
diff --git a/grub-core/fs/ntfscomp.c b/grub-core/fs/ntfscomp.c
index ec359fa9d..9b3b75da4 100644
--- a/grub-core/fs/ntfscomp.c
+++ b/grub-core/fs/ntfscomp.c
@@ -33,8 +33,9 @@ decomp_nextvcn (struct grub_ntfs_comp *cc)
   if (grub_disk_read
       (cc->disk,
        (cc->comp_table[cc->comp_head].next_lcn -
-	(cc->comp_table[cc->comp_head].next_vcn - cc->cbuf_vcn)) * cc->spc, 0,
-       cc->spc << GRUB_NTFS_BLK_SHR, cc->cbuf))
+	(cc->comp_table[cc->comp_head].next_vcn - cc->cbuf_vcn)) << cc->log_spc,
+       0,
+       1 << (cc->log_spc + GRUB_NTFS_BLK_SHR), cc->cbuf))
     return grub_errno;
   cc->cbuf_vcn++;
   if ((cc->cbuf_vcn >= cc->comp_table[cc->comp_head].next_vcn))
@@ -46,7 +47,7 @@ decomp_nextvcn (struct grub_ntfs_comp *cc)
 static grub_err_t
 decomp_getch (struct grub_ntfs_comp *cc, unsigned char *res)
 {
-  if (cc->cbuf_ofs >= (cc->spc << GRUB_NTFS_BLK_SHR))
+  if (cc->cbuf_ofs >= (1U << (cc->log_spc + GRUB_NTFS_BLK_SHR)))
     {
       if (decomp_nextvcn (cc))
 	return grub_errno;
@@ -159,7 +160,7 @@ decomp_block (struct grub_ntfs_comp *cc, char *dest)
     {
       int n;
 
-      n = (cc->spc << GRUB_NTFS_BLK_SHR) - cc->cbuf_ofs;
+      n = (1 << (cc->log_spc + GRUB_NTFS_BLK_SHR)) - cc->cbuf_ofs;
       if (n > cnt)
 	n = cnt;
       if ((dest) && (n))
@@ -178,7 +179,7 @@ decomp_block (struct grub_ntfs_comp *cc, char *dest)
 static grub_err_t
 read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 {
-  int cpb = GRUB_NTFS_COM_SEC / ctx->comp.spc;
+  int log_cpb = GRUB_NTFS_LOG_COM_SEC - ctx->comp.log_spc;
 
   while (num)
     {
@@ -192,7 +193,7 @@ read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 	    return grub_error (GRUB_ERR_BAD_FS, "invalid compression block");
 	  ctx->comp.comp_head = ctx->comp.comp_tail = 0;
 	  ctx->comp.cbuf_vcn = ctx->target_vcn;
-	  ctx->comp.cbuf_ofs = (ctx->comp.spc << GRUB_NTFS_BLK_SHR);
+	  ctx->comp.cbuf_ofs = (1 << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR));
 	  if (ctx->target_vcn >= ctx->next_vcn)
 	    {
 	      if (grub_ntfs_read_run_list (ctx))
@@ -211,14 +212,14 @@ read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 	    }
 	}
 
-      nn = (16 - (unsigned) (ctx->target_vcn & 0xF)) / cpb;
+      nn = (16 - (unsigned) (ctx->target_vcn & 0xF)) >> log_cpb;
       if (nn > num)
 	nn = num;
       num -= nn;
 
       if (ctx->flags & GRUB_NTFS_RF_BLNK)
 	{
-	  ctx->target_vcn += nn * cpb;
+	  ctx->target_vcn += nn << log_cpb;
 	  if (ctx->comp.comp_tail == 0)
 	    {
 	      if (buf)
@@ -241,7 +242,7 @@ read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 	}
       else
 	{
-	  nn *= cpb;
+	  nn <<= log_cpb;
 	  while ((ctx->comp.comp_head < ctx->comp.comp_tail) && (nn))
 	    {
 	      grub_disk_addr_t tt;
@@ -258,10 +259,10 @@ read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 		      (ctx->comp.disk,
 		       (ctx->comp.comp_table[ctx->comp.comp_head].next_lcn -
 			(ctx->comp.comp_table[ctx->comp.comp_head].next_vcn -
-			 ctx->target_vcn)) * ctx->comp.spc, 0,
-		       tt * (ctx->comp.spc << GRUB_NTFS_BLK_SHR), buf))
+			 ctx->target_vcn)) << ctx->comp.log_spc, 0,
+		       tt << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR), buf))
 		    return grub_errno;
-		  buf += tt * (ctx->comp.spc << GRUB_NTFS_BLK_SHR);
+		  buf += tt << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR);
 		}
 	      nn -= tt;
 	      if (ctx->target_vcn >=
@@ -275,10 +276,10 @@ read_block (struct grub_ntfs_rlst *ctx, char *buf, grub_size_t num)
 		  if (grub_disk_read
 		      (ctx->comp.disk,
 		       (ctx->target_vcn - ctx->curr_vcn +
-			ctx->curr_lcn) * ctx->comp.spc, 0,
-		       nn * (ctx->comp.spc << GRUB_NTFS_BLK_SHR), buf))
+			ctx->curr_lcn) << ctx->comp.log_spc, 0,
+		       nn << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR), buf))
 		    return grub_errno;
-		  buf += nn * (ctx->comp.spc << GRUB_NTFS_BLK_SHR);
+		  buf += nn << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR);
 		}
 	      ctx->target_vcn += nn;
 	    }
@@ -294,7 +295,7 @@ ntfscomp (struct grub_ntfs_attr *at, char *dest, grub_disk_addr_t ofs,
   grub_err_t ret;
 
   ctx->comp.comp_head = ctx->comp.comp_tail = 0;
-  ctx->comp.cbuf = grub_malloc ((ctx->comp.spc) << GRUB_NTFS_BLK_SHR);
+  ctx->comp.cbuf = grub_malloc (1 << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR));
   if (!ctx->comp.cbuf)
     return 0;
 
@@ -304,7 +305,7 @@ ntfscomp (struct grub_ntfs_attr *at, char *dest, grub_disk_addr_t ofs,
 
   if ((vcn > ctx->target_vcn) &&
       (read_block
-       (ctx, NULL, ((vcn - ctx->target_vcn) * ctx->comp.spc) / GRUB_NTFS_COM_SEC)))
+       (ctx, NULL, (vcn - ctx->target_vcn) >> (GRUB_NTFS_LOG_COM_SEC - ctx->comp.log_spc))))
     {
       ret = grub_errno;
       goto quit;
@@ -314,7 +315,7 @@ ntfscomp (struct grub_ntfs_attr *at, char *dest, grub_disk_addr_t ofs,
     {
       grub_uint32_t t, n, o;
 
-      t = ctx->target_vcn * (ctx->comp.spc << GRUB_NTFS_BLK_SHR);
+      t = ctx->target_vcn << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR);
       if (read_block (ctx, at->sbuf, 1))
 	{
 	  ret = grub_errno;
@@ -346,7 +347,7 @@ ntfscomp (struct grub_ntfs_attr *at, char *dest, grub_disk_addr_t ofs,
     {
       grub_uint32_t t;
 
-      t = ctx->target_vcn * (ctx->comp.spc << GRUB_NTFS_BLK_SHR);
+      t = ctx->target_vcn << (ctx->comp.log_spc + GRUB_NTFS_BLK_SHR);
       if (read_block (ctx, at->sbuf, 1))
 	{
 	  ret = grub_errno;
diff --git a/include/grub/ntfs.h b/include/grub/ntfs.h
index 093534205..cc28a01e4 100644
--- a/include/grub/ntfs.h
+++ b/include/grub/ntfs.h
@@ -87,6 +87,7 @@ enum
 #define GRUB_NTFS_COM_LEN		4096
 #define GRUB_NTFS_COM_LOG_LEN	12
 #define GRUB_NTFS_COM_SEC		(GRUB_NTFS_COM_LEN >> GRUB_NTFS_BLK_SHR)
+#define GRUB_NTFS_LOG_COM_SEC		(GRUB_NTFS_COM_LOG_LEN - GRUB_NTFS_BLK_SHR)
 
 enum
   {
@@ -156,7 +157,7 @@ struct grub_ntfs_data
   grub_disk_t disk;
   grub_uint32_t mft_size;
   grub_uint32_t idx_size;
-  grub_uint32_t spc;
+  int log_spc;
   grub_uint32_t mft_start;
   grub_uint64_t uuid;
 };
@@ -172,7 +173,8 @@ struct grub_ntfs_comp
   grub_disk_t disk;
   int comp_head, comp_tail;
   struct grub_ntfs_comp_table_element comp_table[16];
-  grub_uint32_t cbuf_ofs, cbuf_vcn, spc;
+  grub_uint32_t cbuf_ofs, cbuf_vcn;
+  int log_spc;
   char *cbuf;
 };