From db6c4f54a2036210c1f5c5aed9aa6c210aaae0ba Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Sun, 6 Dec 2020 09:17:50 +1000
Subject: [PATCH] emory/chunk/map: move chunking to a free function

---
 emory/chunk/map.cpp | 36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/emory/chunk/map.cpp b/emory/chunk/map.cpp
index bdcebf9..f14601f 100644
--- a/emory/chunk/map.cpp
+++ b/emory/chunk/map.cpp
@@ -16,13 +16,17 @@ using emory::chunk::map;
 
 
 ///////////////////////////////////////////////////////////////////////////////
-map::map (
-    cruft::view<u08 const *> src,
+template <typename HashT, typename OutputT>
+static
+OutputT
+find_chunks (
+    OutputT &&dst,
+    cruft::view<u08 const*> src,
     emory::chunk::params const &p
 ) {
     using hash_type = cruft::hash::buzhash<u64>;
     if (src.size () < p.window)
-        return;
+        return dst;
 
     using digest_type = hash_type::digest_type ;
     digest_type const mask = ~digest_type (0) >> (sizeof (digest_type) * 8 - p.bits);
@@ -39,20 +43,20 @@ map::map (
         for ( ; cursor < src.end () - p.window; ++cursor) {
             if (likely (hash_state & mask)) {
                 hash_state = cruft::rotatel (hash_state, 1)
-                           ^ cruft::rotatel (u64 (*(cursor - p.window)), p.window)
-                           ^ *cursor;
+                             ^ cruft::rotatel (u64 (*(cursor - p.window)), p.window)
+                             ^ *cursor;
                 continue;
             }
 
             cruft::view<u08 const*> const region { start, cursor };
 
-            elements.push_back ({
+            *dst = {
                 .offset = {
                     std::distance (src.begin (), start),
                     std::distance (src.begin (), cursor)
                 },
-                .digest = static_hash {} (region)
-            });
+                .digest = HashT {} (region)
+            };
 
             start = cursor;
             break;
@@ -62,12 +66,22 @@ map::map (
     if (start != src.end ()) {
         cruft::view<u08 const*> const region { start, src.end () };
 
-        elements.push_back ({
+        *dst++ = {
             .offset = {
                 std::distance (src.begin (), start),
                 std::distance (src.begin (), src.end ())
             },
-            .digest = static_hash {} (region)
-        });
+            .digest = HashT {} (region)
+        };
     }
+
+    return dst;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+map::map (
+    cruft::view<u08 const *> src,
+    emory::chunk::params const &p
+) {
+    ::find_chunks<static_hash> (std::back_inserter (elements), src, p);
 }