=== modified file 'src/buffer.c'
--- src/buffer.c	2014-03-15 11:16:12 +0000
+++ src/buffer.c	2014-03-17 14:42:01 +0000
@@ -573,6 +573,7 @@
   BUF_END_UNCHANGED (b) = 0;
   BUF_BEG_UNCHANGED (b) = 0;
   *(BUF_GPT_ADDR (b)) = *(BUF_Z_ADDR (b)) = 0; /* Put an anchor '\0'.  */
+  BUF_NL (b) = 0;
   b->text->inhibit_shrinking = false;
   b->text->redisplay = false;
 

=== modified file 'src/buffer.h'
--- src/buffer.h	2014-01-01 07:43:34 +0000
+++ src/buffer.h	2014-03-17 14:42:01 +0000
@@ -91,6 +91,9 @@
 /* Modification count as of last visit or save.  */
 #define SAVE_MODIFF (current_buffer->text->save_modiff)
 
+/* How many '\n' in the buffer.  */
+#define NL (current_buffer->text->nl)
+
 /* BUFFER_CEILING_OF (resp. BUFFER_FLOOR_OF), when applied to n, return
    the max (resp. min) p such that
 
@@ -183,6 +186,9 @@
 /* FIXME: should we move this into ->text->auto_save_modiff?  */
 #define BUF_AUTOSAVE_MODIFF(buf) ((buf)->auto_save_modified)
 
+/* How many '\n' in the buffer.  */
+#define BUF_NL(buf) ((buf)->text->nl)
+
 /* Compaction count.  */
 #define BUF_COMPACT(buf) ((buf)->text->compact)
 
@@ -463,6 +469,9 @@
     /* Properties of this buffer's text.  */
     INTERVAL intervals;
 
+    /* How many '\n' in this buffer's text.  */
+    ptrdiff_t nl;
+
     /* The markers that refer to this buffer.
        This is actually a single marker ---
        successive elements in its marker `chain'

=== modified file 'src/insdel.c'
--- src/insdel.c	2014-01-01 17:44:48 +0000
+++ src/insdel.c	2014-03-17 14:55:57 +0000
@@ -560,7 +560,20 @@
       return to_addr - initial_to_addr;
     }
 }
-
+
+/* Count '\n' in [PTR..PTR + NBYTES).  */
+
+static ptrdiff_t
+count_newlines (const char *ptr, ptrdiff_t nbytes)
+{
+  const char *p = ptr;
+  ptrdiff_t count = 0, restbytes = nbytes;
+
+  while (restbytes > 0 && (p = memchr (p, '\n', restbytes)))
+    p++, count++, restbytes = nbytes - (p - ptr);
+  return count;
+}
+
 /* Insert a string of specified length before point.
    This function judges multibyteness based on
    enable_multibyte_characters in the current buffer;
@@ -814,6 +827,9 @@
   MODIFF++;
   CHARS_MODIFF = MODIFF;
 
+  /* Count newlines in new text.  */
+  NL += count_newlines (string, nbytes);
+
   memcpy (GPT_ADDR, string, nbytes);
 
   GAP_SIZE -= nbytes;
@@ -924,6 +940,9 @@
     make_gap (outgoing_nbytes - GAP_SIZE);
   UNGCPRO;
 
+  /* Count newlines in string text.  */
+  NL += count_newlines (SSDATA (string) + pos_byte, nbytes);
+
   /* Copy the string text into the buffer, perhaps converting
      between single-byte and multibyte.  */
   copy_text (SDATA (string) + pos_byte, GPT_ADDR, nbytes,
@@ -1001,6 +1020,11 @@
   record_insert (GPT, nchars);
   MODIFF++;
 
+  /* Add newlines from new text.  */
+  NL += count_newlines (text_at_gap_tail
+			? (char *) GAP_END_ADDR - nbytes
+			: (char *) GPT_ADDR, nbytes);
+
   GAP_SIZE -= nbytes;
   if (! text_at_gap_tail)
     {
@@ -1138,6 +1162,9 @@
     emacs_abort ();
 #endif
 
+  /* Add newlines from gap.  */
+  NL += count_newlines ((char *) GPT_ADDR, outgoing_nbytes);
+
   record_insert (PT, nchars);
   MODIFF++;
   CHARS_MODIFF = MODIFF;
@@ -1340,6 +1367,9 @@
      combining.  */
   if (! EQ (BVAR (current_buffer, undo_list), Qt))
     deletion = make_buffer_string_both (from, from_byte, to, to_byte, 1);
+  
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
 
   GAP_SIZE += nbytes_del;
   ZV -= nchars_del;
@@ -1360,6 +1390,9 @@
   if (GAP_SIZE < outgoing_insbytes)
     make_gap (outgoing_insbytes - GAP_SIZE);
 
+  /* Add newlines from string text.  */
+  NL += count_newlines (SSDATA (new), insbytes);
+
   /* Copy the string text into the buffer, perhaps converting
      between single-byte and multibyte.  */
   copy_text (SDATA (new), GPT_ADDR, insbytes,
@@ -1470,6 +1503,9 @@
   if (to < GPT)
     gap_left (to, to_byte, 0);
 
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
+
   GAP_SIZE += nbytes_del;
   ZV -= nchars_del;
   Z -= nchars_del;
@@ -1489,6 +1525,9 @@
   if (GAP_SIZE < insbytes)
     make_gap (insbytes - GAP_SIZE);
 
+  /* Add newlines from replacement text.  */
+  NL += count_newlines (ins, insbytes);
+
   /* Copy the replacement text into the buffer.  */
   memcpy (GPT_ADDR, ins, insbytes);
 
@@ -1737,6 +1776,9 @@
      adjusting the markers that bound the overlays.  */
   adjust_overlays_for_delete (from, nchars_del);
 
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
+
   GAP_SIZE += nbytes_del;
   ZV_BYTE -= nbytes_del;
   Z_BYTE -= nbytes_del;