Allow odd/even modifiers in numeric range (fixes #364)

libqpdf/QUtil.cc

@@ -1116,6 +1116,8 @@ QUtil::parse_numrange(char const* range, int max)
         std::vector<int> work;
         static int const comma = -1;
         static int const dash = -2;
+        size_t start_idx = 0;
+        size_t skip = 1;
 
         enum { st_top,
                st_in_number,
@@ -1182,6 +1184,14 @@ QUtil::parse_numrange(char const* range, int max)
                     work.push_back(dash);
                 }
             }
+            else if (ch == ':')
+            {
+                if (! ((state == st_in_number) || (state == st_after_number)))
+                {
+                    throw std::runtime_error("unexpected colon");
+                }
+                break;
+            }
             else
             {
                 throw std::runtime_error("unexpected character");
@@ -1197,6 +1207,22 @@ QUtil::parse_numrange(char const* range, int max)
         {
             throw std::runtime_error("number expected");
         }
+        if (*p == ':')
+        {
+            if (strcmp(p, ":odd") == 0)
+            {
+                skip = 2;
+            }
+            else if (strcmp(p, ":even") == 0)
+            {
+                skip = 2;
+                start_idx = 1;
+            }
+            else
+            {
+                throw std::runtime_error("unexpected even/odd modifier");
+            }
+        }
 
         p = 0;
         for (size_t i = 0; i < work.size(); i += 2)
@@ -1245,6 +1271,15 @@ QUtil::parse_numrange(char const* range, int max)
                 }
             }
         }
+        if ((start_idx > 0) || (skip != 1))
+        {
+            auto t = result;
+            result.clear();
+            for (size_t i = start_idx; i < t.size(); i += skip)
+            {
+                result.push_back(t.at(i));
+            }
+        }
     }
     catch (std::runtime_error const& e)
     {

libtests/qtest/numrange.test

@@ -49,6 +49,24 @@ my @nrange_tests = (
      "numeric range r1-r15" .
      " -> 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1",
      0],
+    ["1-10:quack",
+     "error at * in numeric range 1-10*:quack: unexpected even/odd modifier",
+     2],
+    ["1-10:",
+     "error at * in numeric range 1-10*:: unexpected even/odd modifier",
+     2],
+    ["1-10,r:",
+     "error at * in numeric range 1-10,r*:: unexpected even/odd modifier",
+     2],
+    ["1-10,:",
+     "error at * in numeric range 1-10,*:: unexpected colon",
+     2],
+    ["1-6,8-12:odd",
+     "numeric range 1-6,8-12:odd -> 1 3 5 8 10 12",
+     0],
+    ["1-6,8-12:even",
+     "numeric range 1-6,8-12:even -> 2 4 6 9 11",
+     0],
     );
 foreach my $d (@nrange_tests)
 {

manual/qpdf-manual.xml

@@ -1391,9 +1391,12 @@ make
     <literal>r3-r1</literal> would be the last three pages of the
     document. Pages can appear in any order. Ranges can appear with a
     high number followed by a low number, which causes the pages to
-    appear in reverse. Repeating a number will cause an error, but you
-    can use the workaround discussed above should you really want to
-    include the same page twice.
+    appear in reverse. Numbers may be repeated in a page range. A page
+    range may be optionally appended with <literal>:even</literal> or
+    <literal>:odd</literal> to indicate only the even or odd pages in
+    the given range. Note that even and odd refer to the positions
+    within the specified, range, not whether the original number is
+    even or odd.
    </para>
    <para>
     Example page ranges:
@@ -1420,6 +1423,18 @@ make
        in reverse order
       </para>
      </listitem>
+     <listitem>
+      <para>
+       <literal>1-20:even</literal>: even pages from 2 to 20
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       <literal>5,7-9,12:odd</literal>: pages 5, 8, and, 12, which are
+       the pages in odd positions from among the original range, which
+       represents pages 5, 7, 8, 9, and 12.
+      </para>
+     </listitem>
     </itemizedlist>
    </para>
    <para>
@@ -4663,6 +4678,13 @@ print "\n";
           <xref linkend="ref.crypto"/>.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          Allow <literal>:even</literal> or <literal>:odd</literal> to
+          be appended to numeric ranges for specification of the even
+          or odd pages from among the pages specified in the range.
+         </para>
+        </listitem>
        </itemizedlist>
       </listitem>
      </itemizedlist>

qpdf/qpdf.cc

@@ -1286,8 +1286,9 @@ ArgParser::argHelp()
         << "to count from the end, so \"r3-r1\" would be the last three pages of the\n"
         << "document.  Pages can appear in any order.  Ranges can appear with a\n"
         << "high number followed by a low number, which causes the pages to appear in\n"
-        << "reverse.  Repeating a number will cause an error, but the manual discusses\n"
-        << "a workaround should you really want to include the same page twice.\n"
+        << "reverse.  Numbers may be repeated.  A page range may be appended with :odd\n"
+        << "to indicate odd pages in the selected range or :even to indicate even\n"
+        << "pages.\n"
         << "\n"
         << "If the page range is omitted, the range of 1-z is assumed.  qpdf decides\n"
         << "that the page range is omitted if the range argument is either -- or a\n"