diff --git a/src/hb-ot-layout-gpos-table.hh b/src/hb-ot-layout-gpos-table.hh
index cff1deb3a..d24a06138 100644
--- a/src/hb-ot-layout-gpos-table.hh
+++ b/src/hb-ot-layout-gpos-table.hh
@@ -629,21 +629,21 @@ struct PairPosFormat1
   inline bool apply (hb_apply_context_t *c) const
   {
     TRACE_APPLY ();
-    unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-    if (unlikely (c->buffer->idx + 2 > end))
+    unsigned int j = c->buffer->idx;
+    unsigned int end = MIN (c->buffer->len, j + c->context_length);
+    if (unlikely (j >= end))
       return false;
 
-    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->idx].codepoint);
+    unsigned int index = (this+coverage) (c->buffer->info[j].codepoint);
     if (likely (index == NOT_COVERED))
       return false;
 
-    unsigned int j = c->buffer->idx + 1;
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL))
+    do
     {
+      j++;
       if (unlikely (j == end))
 	return false;
-      j++;
-    }
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL));
 
     return (this+pairSet[index]).apply (c, &valueFormat1, j);
   }
@@ -691,21 +691,21 @@ struct PairPosFormat2
   inline bool apply (hb_apply_context_t *c) const
   {
     TRACE_APPLY ();
-    unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-    if (unlikely (c->buffer->idx + 2 > end))
+    unsigned int j = c->buffer->idx;
+    unsigned int end = MIN (c->buffer->len, j + c->context_length);
+    if (unlikely (j >= end))
       return false;
 
-    unsigned int index = (this+coverage) (c->buffer->info[c->buffer->idx].codepoint);
+    unsigned int index = (this+coverage) (c->buffer->info[j].codepoint);
     if (likely (index == NOT_COVERED))
       return false;
 
-    unsigned int j = c->buffer->idx + 1;
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL))
+    do
     {
+      j++;
       if (unlikely (j == end))
 	return false;
-      j++;
-    }
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL));
 
     unsigned int len1 = valueFormat1.get_len ();
     unsigned int len2 = valueFormat2.get_len ();
@@ -846,21 +846,21 @@ struct CursivePosFormat1
     if (c->property & HB_OT_LAYOUT_GLYPH_CLASS_MARK)
       return false;
 
-    unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-    if (unlikely (c->buffer->idx + 2 > end))
+    unsigned int j = c->buffer->idx;
+    unsigned int end = MIN (c->buffer->len, j + c->context_length);
+    if (unlikely (j >= end))
       return false;
 
-    const EntryExitRecord &this_record = entryExitRecord[(this+coverage) (c->buffer->info[c->buffer->idx].codepoint)];
+    const EntryExitRecord &this_record = entryExitRecord[(this+coverage) (c->buffer->info[j].codepoint)];
     if (!this_record.exitAnchor)
       return false;
 
-    unsigned int j = c->buffer->idx + 1;
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL))
+    do
     {
+      j++;
       if (unlikely (j == end))
 	return false;
-      j++;
-    }
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL));
 
     const EntryExitRecord &next_record = entryExitRecord[(this+coverage) (c->buffer->info[j].codepoint)];
     if (!next_record.entryAnchor)
diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 4c423cce1..46314ade9 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -343,24 +343,25 @@ struct Ligature
   inline bool apply (hb_apply_context_t *c) const
   {
     TRACE_APPLY ();
-    unsigned int i, j;
+    unsigned int i;
+    unsigned int j = c->buffer->idx;
     unsigned int count = component.len;
-    unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-    if (unlikely (count < 2 || c->buffer->idx + count > end))
+    unsigned int end = MIN (c->buffer->len, j + c->context_length);
+    if (unlikely (count < 2 || j >= end))
       return false;
 
     bool first_was_mark = (c->property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
     bool found_non_mark = false;
 
-    for (i = 1, j = c->buffer->idx + 1; i < count; i++, j++)
+    for (i = 1; i < count; i++)
     {
       unsigned int property;
-      while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, &property))
+      do
       {
-	if (unlikely (j + count - i == end))
-	  return false;
 	j++;
-      }
+	if (unlikely (j == end))
+	  return false;
+      } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, &property));
 
       found_non_mark |= !(property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
 
@@ -376,9 +377,9 @@ struct Ligature
     c->buffer->info[c->buffer->idx].lig_comp() = 0;
     c->buffer->info[c->buffer->idx].lig_id() = lig_id;
 
-    if (j == c->buffer->idx + i) /* No input glyphs skipped */
+    if (j < c->buffer->idx + count) /* No input glyphs skipped */
     {
-      c->replace_glyphs_be16 (i, 1, (const uint16_t *) &ligGlyph);
+      c->replace_glyphs_be16 (count, 1, (const uint16_t *) &ligGlyph);
     }
     else
     {
diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 14979e16e..5912924a1 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -132,25 +132,26 @@ static inline bool match_input (hb_apply_context_t *c,
 				const void *match_data,
 				unsigned int *context_length_out)
 {
-  unsigned int i, j;
-  unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-  if (unlikely (c->buffer->idx + count > end))
+  unsigned int i;
+  unsigned int j = c->buffer->idx;
+  unsigned int end = MIN (c->buffer->len, j + c->context_length);
+  if (unlikely (j + count > end))
     return false;
 
-  for (i = 1, j = c->buffer->idx + 1; i < count; i++, j++)
+  for (i = 1; i < count; i++)
   {
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL))
+    do
     {
-      if (unlikely (j + count - i == end))
-	return false;
       j++;
-    }
+      if (unlikely (j >= end))
+	return false;
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL));
 
     if (likely (!match_func (c->buffer->info[j].codepoint, input[i - 1], match_data)))
       return false;
   }
 
-  *context_length_out = j - c->buffer->idx;
+  *context_length_out = j - c->buffer->idx + 1;
 
   return true;
 }
@@ -161,17 +162,16 @@ static inline bool match_backtrack (hb_apply_context_t *c,
 				    match_func_t match_func,
 				    const void *match_data)
 {
-  if (unlikely (c->buffer->backtrack_len () < count))
-    return false;
+  unsigned int j = c->buffer->backtrack_len ();
 
-  for (unsigned int i = 0, j = c->buffer->backtrack_len () - 1; i < count; i++, j--)
+  for (unsigned int i = 0; i < count; i++)
   {
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->out_info[j], c->lookup_props, NULL))
+    do
     {
-      if (unlikely (j + 1 == count - i))
+      if (unlikely (!j))
 	return false;
       j--;
-    }
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->out_info[j], c->lookup_props, NULL));
 
     if (likely (!match_func (c->buffer->out_info[j].codepoint, backtrack[i], match_data)))
       return false;
@@ -187,19 +187,18 @@ static inline bool match_lookahead (hb_apply_context_t *c,
 				    const void *match_data,
 				    unsigned int offset)
 {
-  unsigned int i, j;
+  unsigned int i;
+  unsigned int j = c->buffer->idx + offset - 1;
   unsigned int end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
-  if (unlikely (c->buffer->idx + offset + count > end))
-    return false;
 
-  for (i = 0, j = c->buffer->idx + offset; i < count; i++, j++)
+  for (i = 0; i < count; i++)
   {
-    while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL))
+    do
     {
-      if (unlikely (j + count - i == end))
-	return false;
       j++;
-    }
+      if (unlikely (j >= end))
+	return false;
+    } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[j], c->lookup_props, NULL));
 
     if (likely (!match_func (c->buffer->info[j].codepoint, lookahead[i], match_data)))
       return false;