1 files changed, 88 insertions, 1 deletions
diff --git a/technical/bitmap-format.html b/technical/bitmap-format.html
index 064d14f25..3a06697df 100644
--- a/technical/bitmap-format.html
+++ b/technical/bitmap-format.html
@@ -854,6 +854,33 @@ BITMAP_OPT_HASH_CACHE (0x4):
 </dd>
 </dl></div>
 </li>
+<li>
+<p>
+</p>
+<div class="dlist"><dl>
+<dt class="hdlist1">
+BITMAP_OPT_LOOKUP_TABLE (0x10): 
+</dt>
+<dd>
+<p>
+                If present, the end of the bitmap file contains a table
+                containing a list of <code>N</code> &lt;commit_pos, offset, xor_row&gt;
+                triplets. The format and meaning of the table is described
+                below.
+</p>
+<div class="admonitionblock">
+<table><tr>
+<td class="icon">
+<div class="title">Note</div>
+</td>
+<td class="content">Unlike the xor_offset used to compress an individual bitmap,
+<code>xor_row</code> stores an <strong>absolute</strong> index into the lookup table, not a location
+relative to the current entry.</td>
+</tr></table>
+</div>
+</dd>
+</dl></div>
+</li>
 </ul></div>
 </dd>
 <dt class="hdlist1">
@@ -1116,12 +1143,72 @@ free to do so, but MUST allocate a new header flag (because comparing
 hashes made under two different schemes would be pointless).</p></div>
 </div>
 </div>
+<div class="sect1">
+<h2 id="_commit_lookup_table">Commit lookup table</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the BITMAP_OPT_LOOKUP_TABLE flag is set, the last <code>N * (4 + 8 + 4)</code>
+bytes (preceding the name-hash cache and trailing hash) of the <code>.bitmap</code>
+file contains a lookup table specifying the information needed to get
+the desired bitmap from the entries without parsing previous unnecessary
+bitmaps.</p></div>
+<div class="paragraph"><p>For a <code>.bitmap</code> containing <code>nr_entries</code> reachability bitmaps, the table
+contains a list of <code>nr_entries</code> &lt;commit_pos, offset, xor_row&gt; triplets
+(sorted in the ascending order of <code>commit_pos</code>). The content of i&#8217;th
+triplet is -</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+</p>
+<div class="dlist"><dl>
+<dt class="hdlist1">
+commit_pos (4 byte integer, network byte order): 
+</dt>
+<dd>
+<p>
+        It stores the object position of a commit (in the midx or pack
+        index).
+</p>
+</dd>
+</dl></div>
+</li>
+<li>
+<p>
+</p>
+<div class="dlist"><dl>
+<dt class="hdlist1">
+offset (8 byte integer, network byte order): 
+</dt>
+<dd>
+<p>
+        The offset from which that commit&#8217;s bitmap can be read.
+</p>
+</dd>
+</dl></div>
+</li>
+<li>
+<p>
+</p>
+<div class="dlist"><dl>
+<dt class="hdlist1">
+xor_row (4 byte integer, network byte order): 
+</dt>
+<dd>
+<p>
+        The position of the triplet whose bitmap is used to compress
+        this one, or <code>0xffffffff</code> if no such bitmap exists.
+</p>
+</dd>
+</dl></div>
+</li>
+</ul></div>
+</div>
+</div>
 </div>
 <div id="footnotes"><hr /></div>
 <div id="footer">
 <div id="footer-text">
 Last updated
- 2022-07-11 16:06:18 PDT
+ 2022-09-05 18:35:54 PDT
 </div>
 </div>
 </body>