Fix bug #16830 with slow search for newlines in forward-line.

 src/search.c (find_newline): Speed up the function when using the
 newline cache, by halving the number of calls to
 region_cache_forward and region_cache_backward.

2 files changed, 98 insertions, 16 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 424416398e8..30692059f03 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2014-03-16  Eli Zaretskii  <eliz@gnu.org>
+
+        * search.c (find_newline): Speed up the function when using the
+        newline cache, by halving the number of call to
+        region_cache_forward and region_cache_backward.  (Bug#16830)
+
 2014-03-15  Juanma Barranquero  <lekktu@gmail.com>
 
         * buffer.c (Fset_buffer): Document return value (bug#17015).
diff --git a/src/search.c b/src/search.c
index 40ab5db495a..3de194c5056 100644
--- a/src/search.c
+++ b/src/search.c
@@ -715,19 +715,62 @@ find_newline (ptrdiff_t start, ptrdiff_t start_byte, ptrdiff_t end,
            examine.  */
         ptrdiff_t tem, ceiling_byte = end_byte - 1;
 
-        /* If we're looking for a newline, consult the newline cache
-           to see where we can avoid some scanning.  */
+        /* If we're using the newline cache, consult it to see whether
+           we can avoid some scanning.  */
         if (newline_cache)
           {
             ptrdiff_t next_change;
+            int result = 1;
+
             immediate_quit = 0;
-            while (region_cache_forward
-                   (cache_buffer, newline_cache, start, &next_change))
-              start = next_change;
+            while (start < end && result)
+              {
+                ptrdiff_t lim1;
+
+                result = region_cache_forward (cache_buffer, newline_cache,
+                                               start, &next_change);
+                if (result)
+                  {
+                    start = next_change;
+                    lim1 = next_change = end;
+                  }
+                else
+                  lim1 = min (next_change, end);
+
+                /* The cache returned zero for this region; see if
+                   this is because the region is known and includes
+                   only newlines.  While at that, count any newlines
+                   we bump into, and exit if we found enough off them.  */
+                start_byte = CHAR_TO_BYTE (start);
+                while (start < lim1
+                       && FETCH_BYTE (start_byte) == '\n')
+                  {
+                    start_byte++;
+                    start++;
+                    if (--count == 0)
+                      {
+                        if (bytepos)
+                          *bytepos = start_byte;
+                        return start;
+                      }
+                  }
+                /* If we found a non-newline character before hitting
+                   position where the cache will again return non-zero
+                   (i.e. no newlines beyond that position), it means
+                   this region is not yet known to the cache, and we
+                   must resort to the "dumb loop" method.  */
+                if (start < next_change && !result)
+                  break;
+                result = 1;
+              }
+            if (start >= end)
+              {
+                start = end;
+                start_byte = end_byte;
+                break;
+              }
             immediate_quit = allow_quit;
 
-            start_byte = CHAR_TO_BYTE (start);
-
             /* START should never be after END.  */
             if (start_byte > ceiling_byte)
               start_byte = ceiling_byte;
@@ -762,9 +805,9 @@ find_newline (ptrdiff_t start, ptrdiff_t start_byte, ptrdiff_t end,
               unsigned char *nl = memchr (lim_addr + cursor, '\n', - cursor);
               next = nl ? nl - lim_addr : 0;
 
-              /* If we're looking for newlines, cache the fact that
-                 this line's region is free of them. */
-              if (newline_cache)
+              /* If we're using the newline cache, cache the fact that
+                 the region we just traversed is free of newlines. */
+              if (newline_cache && cursor != next)
                 {
                   know_region_cache (cache_buffer, newline_cache,
                                      BYTE_TO_CHAR (lim_byte + cursor),
@@ -800,14 +843,47 @@ find_newline (ptrdiff_t start, ptrdiff_t start_byte, ptrdiff_t end,
         if (newline_cache)
           {
             ptrdiff_t next_change;
+            int result = 1;
+
             immediate_quit = 0;
-            while (region_cache_backward
-                   (cache_buffer, newline_cache, start, &next_change))
-              start = next_change;
+            while (start > end && result)
+              {
+                ptrdiff_t lim1;
+
+                result = region_cache_backward (cache_buffer, newline_cache,
+                                                start, &next_change);
+                if (result)
+                  {
+                    start = next_change;
+                    lim1 = next_change = end;
+                  }
+                else
+                  lim1 = max (next_change, end);
+                start_byte = CHAR_TO_BYTE (start);
+                while (start > lim1
+                       && FETCH_BYTE (start_byte - 1) == '\n')
+                  {
+                    if (++count == 0)
+                      {
+                        if (bytepos)
+                          *bytepos = start_byte;
+                        return start;
+                      }
+                    start_byte--;
+                    start--;
+                  }
+                if (start > next_change && !result)
+                  break;
+                result = 1;
+              }
+            if (start <= end)
+              {
+                start = end;
+                start_byte = end_byte;
+                break;
+              }
             immediate_quit = allow_quit;
 
-            start_byte = CHAR_TO_BYTE (start);
-
             /* Start should never be at or before end.  */
             if (start_byte <= ceiling_byte)
               start_byte = ceiling_byte + 1;
@@ -840,7 +916,7 @@ find_newline (ptrdiff_t start, ptrdiff_t start_byte, ptrdiff_t end,
 
               /* If we're looking for newlines, cache the fact that
                  this line's region is free of them. */
-              if (newline_cache)
+              if (newline_cache && cursor != prev + 1)
                 {
                   know_region_cache (cache_buffer, newline_cache,
                                      BYTE_TO_CHAR (ceiling_byte + prev + 1),