Implemented first recursive search_n implementation. Add random-access iterator overloads

Author: igaztanaga

include/boost/container/experimental/segmented_search_n.hpp

@@ -32,17 +32,221 @@ FwdIt segmented_search_n
 
 namespace detail_algo {
 
+template <class RAIter, class Size, class T>
+BOOST_CONTAINER_FORCEINLINE
+RAIter segmented_search_n_dispatch
+   (RAIter first, RAIter last, Size count, const T& value,
+    const non_segmented_iterator_tag &, const std::random_access_iterator_tag &)
+{
+   typedef typename iterator_traits<RAIter>::difference_type difference_type;
+
+   const difference_type len = last - first;
+   const difference_type dcount = static_cast<difference_type>(count);
+   if (dcount > len)
+      return last;
+
+   const RAIter scan_end = last - (dcount - 1);
+
+   for (; first < scan_end; ++first) {
+      if (*first == value) {
+         RAIter candidate = first;
+         const RAIter run_end = first + dcount;
+         ++first;
+         BOOST_CONTAINER_SEGMENTED_UNROLL(4)
+         for (; first != run_end; ++first) {
+            if (!(*first == value))
+               goto continue_scan;
+         }
+         return candidate;
+         continue_scan:;
+      }
+   }
+   return last;
+}
+
+template <class FwdIt, class Sent, class Size, class T, class Tag, class Cat>
+typename algo_enable_if_c<
+   !Tag::value || is_sentinel<Sent, FwdIt>::value, FwdIt>::type
+segmented_search_n_dispatch
+   (FwdIt first, Sent last, Size count, const T& value, Tag, Cat)
+{
+   for(; first != last; ++first) {
+      if(*first == value) {
+         FwdIt candidate = first;
+         Size matched = 1;
+         ++first;
+         BOOST_CONTAINER_SEGMENTED_UNROLL(4)
+         for(; matched < count; ++matched, ++first) {
+            if(first == last)
+               return last;
+            if(!(*first == value))
+               goto continue_scan;
+         }
+         return candidate;
+         continue_scan:;
+      }
+   }
+   return last;
+}
+
+// Scans local range [lcur, lend) for search_n, updating cross-segment state.
+// Returns true if a run of 'count' consecutive matches has been completed.
+// On return, lcur is past the last element processed, consecutive/match_start
+// are updated to reflect any partial match at the segment tail.
+template <class LocalIter, class Size, class T, class SegIter, class SegmentIter>
+bool search_n_scan_segment
+   (LocalIter& lcur, LocalIter lend,
+    Size& consecutive, Size count, const T& value,
+    SegIter& match_start, SegmentIter scur,
+    const non_segmented_iterator_tag &, const std::random_access_iterator_tag &src_tag)
+{
+   typedef segmented_iterator_traits<SegIter> seg_traits;
+   typedef typename iterator_traits<LocalIter>::difference_type difference_type;
+
+   while(lcur != lend) {
+      if(consecutive == 0) {
+         // Use find to skip non-matching elements (benefits from RA/vectorization)
+         lcur = (segmented_find_dispatch)(lcur, lend, value, non_segmented_iterator_tag(), src_tag);
+         if(lcur == lend)
+            return false;
+
+         match_start = seg_traits::compose(scur, lcur);
+         consecutive = 1;
+         if(consecutive == count)
+            return true;
+         ++lcur;
+      }
+      else {
+         // Verify consecutive matches; we know exactly how many to check
+         const difference_type need   = static_cast<difference_type>(count - consecutive);
+         const difference_type avail  = lend - lcur;
+         const difference_type ncheck = need < avail ? need : avail;
+         const LocalIter check_end = lcur + ncheck;
+
+         for(; lcur != check_end; ++lcur) {
+            if(!(*lcur == value)) {
+               consecutive = 0;
+               ++lcur;
+               break;
+            }
+            ++consecutive;
+            if(consecutive == count)
+               return true;
+         }
+      }
+   }
+   return false;
+}
+
+template <class LocalIter, class Size, class T, class SegIter, class SegmentIter, class Tag, class Cat>
+typename algo_enable_if_c<!Tag::value, bool>::type
+search_n_scan_segment
+   (LocalIter& lcur, LocalIter lend,
+    Size& consecutive, Size count, const T& value,
+    SegIter& match_start, SegmentIter scur, Tag, Cat)
+{
+   typedef segmented_iterator_traits<SegIter> seg_traits;
+
+   for(; lcur != lend; ++lcur) {
+      if(*lcur == value) {
+         if(consecutive == 0)
+            match_start = seg_traits::compose(scur, lcur);
+         ++consecutive;
+         if(consecutive == count)
+            return true;
+      }
+      else {
+         consecutive = 0;
+      }
+   }
+   return false;
+}
+
+// Recursively segmented local iterators: decompose into sub-segments
+// so that the innermost (non-segmented) level gets RA optimization.
+// Uses lend as sentinel to detect whether local_match was set by inner calls
+// (a match position is always before lend).
+template <class LocalIter, class Size, class T, class SegIter, class SegmentIter, class Cat>
+bool search_n_scan_segment
+   (LocalIter& lcur, LocalIter lend,
+    Size& consecutive, Size count, const T& value,
+    SegIter& match_start, SegmentIter scur,
+    segmented_iterator_tag, Cat)
+{
+   typedef segmented_iterator_traits<SegIter>     outer_traits;
+   typedef segmented_iterator_traits<LocalIter>   local_traits;
+   typedef typename local_traits::segment_iterator  sub_seg_iter;
+   typedef typename local_traits::local_iterator    sub_local_iter;
+   typedef typename segmented_iterator_traits<sub_local_iter>::is_segmented_iterator sub_is_seg_t;
+   typedef typename iterator_traits<sub_local_iter>::iterator_category sub_cat_t;
+
+   sub_seg_iter   sub_scur  = local_traits::segment(lcur);
+   sub_seg_iter   sub_slast = local_traits::segment(lend);
+   sub_local_iter sub_lcur  = local_traits::local(lcur);
+
+   LocalIter local_match = lend;
+
+   if(sub_scur == sub_slast) {
+      sub_local_iter sub_lend = local_traits::local(lend);
+      if(search_n_scan_segment(sub_lcur, sub_lend, consecutive, count, value,
+                               local_match, sub_scur, sub_is_seg_t(), sub_cat_t())) {
+         if(local_match != lend)
+            match_start = outer_traits::compose(scur, local_match);
+         lcur = lend;
+         return true;
+      }
+   }
+   else {
+      {
+         sub_local_iter sub_lend = local_traits::end(sub_scur);
+         if(search_n_scan_segment(sub_lcur, sub_lend, consecutive, count, value,
+                                  local_match, sub_scur, sub_is_seg_t(), sub_cat_t())) {
+            if(local_match != lend)
+               match_start = outer_traits::compose(scur, local_match);
+            lcur = lend;
+            return true;
+         }
+      }
+      for(++sub_scur; sub_scur != sub_slast; ++sub_scur) {
+         sub_lcur = local_traits::begin(sub_scur);
+         sub_local_iter sub_le = local_traits::end(sub_scur);
+         if(search_n_scan_segment(sub_lcur, sub_le, consecutive, count, value,
+                                  local_match, sub_scur, sub_is_seg_t(), sub_cat_t())) {
+            if(local_match != lend)
+               match_start = outer_traits::compose(scur, local_match);
+            lcur = lend;
+            return true;
+         }
+      }
+      {
+         sub_lcur = local_traits::begin(sub_scur);
+         sub_local_iter sub_ll = local_traits::local(lend);
+         if(search_n_scan_segment(sub_lcur, sub_ll, consecutive, count, value,
+                                  local_match, sub_scur, sub_is_seg_t(), sub_cat_t())) {
+            if(local_match != lend)
+               match_start = outer_traits::compose(scur, local_match);
+            lcur = lend;
+            return true;
+         }
+      }
+   }
+   if(local_match != lend)
+      match_start = outer_traits::compose(scur, local_match);
+   lcur = lend;
+   return false;
+}
+
 // Non-recursive: must carry cross-segment state (consecutive count,
 // match_start) to track runs that span segment boundaries.
-template <class SegIter, class Size, class T>
+template <class SegIter, class Size, class T, class Cat>
 SegIter segmented_search_n_dispatch
-   (SegIter first, SegIter last, Size count, const T& value, segmented_iterator_tag)
+   (SegIter first, SegIter last, Size count, const T& value, segmented_iterator_tag, Cat)
 {
-   if(count <= 0) return first;
-
    typedef segmented_iterator_traits<SegIter> traits;
    typedef typename traits::segment_iterator  segment_iterator;
    typedef typename traits::local_iterator    local_iterator;
+   typedef typename segmented_iterator_traits<local_iterator>::is_segmented_iterator is_local_seg_t;
+   typedef typename iterator_traits<local_iterator>::iterator_category local_cat_t;
 
    Size consecutive = 0;
    SegIter match_start = first;
@@ -54,94 +258,30 @@ SegIter segmented_search_n_dispatch
 
    if(scur == slast) {
       local_iterator lend = traits::local(last);
-      for(; lcur != lend; ++lcur) {
-         if(*lcur == value) {
-            if(consecutive == 0)
-               match_start = traits::compose(scur, lcur);
-            ++consecutive;
-            if(consecutive == count)
-               return match_start;
-         }
-         else {
-            consecutive = 0;
-         }
-      }
+      if(search_n_scan_segment(lcur, lend, consecutive, count, value,
+                               match_start, scur, is_local_seg_t(), local_cat_t()))
+         return match_start;
    }
    else {
       {
          local_iterator lend = traits::end(scur);
-         for(; lcur != lend; ++lcur) {
-            if(*lcur == value) {
-               if(consecutive == 0)
-                  match_start = traits::compose(scur, lcur);
-               ++consecutive;
-               if(consecutive == count)
-                  return match_start;
-            }
-            else {
-               consecutive = 0;
-            }
-         }
+         if(search_n_scan_segment(lcur, lend, consecutive, count, value,
+                                  match_start, scur, is_local_seg_t(), local_cat_t()))
+            return match_start;
       }
       for(++scur; scur != slast; ++scur) {
-         local_iterator lb = traits::begin(scur);
+         lcur = traits::begin(scur);
          local_iterator le = traits::end(scur);
-         for(lcur = lb; lcur != le; ++lcur) {
-            if(*lcur == value) {
-               if(consecutive == 0)
-                  match_start = traits::compose(scur, lcur);
-               ++consecutive;
-               if(consecutive == count)
-                  return match_start;
-            }
-            else {
-               consecutive = 0;
-            }
-         }
+         if(search_n_scan_segment(lcur, le, consecutive, count, value,
+                                  match_start, scur, is_local_seg_t(), local_cat_t()))
+            return match_start;
       }
       {
-         local_iterator lb = traits::begin(scur);
+         lcur = traits::begin(scur);
          local_iterator ll = traits::local(last);
-         for(lcur = lb; lcur != ll; ++lcur) {
-            if(*lcur == value) {
-               if(consecutive == 0)
-                  match_start = traits::compose(scur, lcur);
-               ++consecutive;
-               if(consecutive == count)
-                  return match_start;
-            }
-            else {
-               consecutive = 0;
-            }
-         }
-      }
-   }
-   return last;
-}
-
-template <class FwdIt, class Sent, class Size, class T, class Tag>
-typename algo_enable_if_c<
-   !Tag::value || is_sentinel<Sent, FwdIt>::value, FwdIt>::type
-segmented_search_n_dispatch
-   (FwdIt first, Sent last, Size count, const T& value, Tag)
-{
-   if(count <= 0)
-      return first;
-
-   for(; first != last; ++first) {
-      if(*first == value) {
-         FwdIt candidate = first;
-         Size matched = 1;
-         FwdIt it = first;
-         ++it;
-         for(; matched < count; ++matched, ++it) {
-            if(it == last)
-               return last;
-            if(!(*it == value))
-               break;
-         }
-         if(matched == count)
-            return candidate;
+         if(search_n_scan_segment(lcur, ll, consecutive, count, value,
+                                  match_start, scur, is_local_seg_t(), local_cat_t()))
+            return match_start;
       }
    }
    return last;
@@ -155,12 +295,15 @@ template <class FwdIt, class Sent, class Size, class T>
 inline FwdIt segmented_search_n
    (FwdIt first, Sent last, Size count, const T& value)
 {
-   if(count == 1)
+   if (BOOST_UNLIKELY(count <= 0))
+      return first;
+   else if(BOOST_UNLIKELY(count == 1))
       return (segmented_find)(first, last, value);
 
    typedef segmented_iterator_traits<FwdIt> traits;
    return detail_algo::segmented_search_n_dispatch
-      (first, last, count, value, typename traits::is_segmented_iterator());
+      (first, last, count, value, typename traits::is_segmented_iterator(),
+       typename iterator_traits<FwdIt>::iterator_category());
 }
 
 } // namespace container