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diff --git a/src/intervals.cc b/src/intervals.cc
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+/***************************************************************************
+ *   Copyright (C) 2017-2018 by Hans-Peter Deifel                          *
+ *   hpd@hpdeifel.de                                                       *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   This program is distributed in the hope that it will be useful,       *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU General Public License for more details.                          *
+ *                                                                         *
+ *   You should have received a copy of the GNU General Public License     *
+ *   along with this program; if not, write to the                         *
+ *   Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,      *
+ *   Boston, MA 02110-1301 USA.                                            *
+ ***************************************************************************/
+
+#include "intervals.h"
+
+#include <algorithm>
+#include <sstream>
+#include <iostream>
+#include <stdexcept>
+
+#include "output.h"
+
+// The interval container data structure could be much more sophisticated (e.g
+// by using interval trees or even sorted lists), but as the number of intervals
+// in typical use cases is small, this shouldn't make much difference and could
+// actually be harmful.
+//
+// tl;dr Measure before you optimize
+
+void IntervalContainer::addInterval(Interval i) {
+	intervals.push_back(i);
+}
+
+bool IntervalContainer::contains(int element) const {
+	// We interpret the empty container as one interval containing
+	// everything. This makes sense in the pdfgrep case: If the user doesn't
+	// restrict the intervals she want's all pages to be searched.
+	if (intervals.empty())
+		return true;
+
+	auto predicate = [=](const Interval &a) {return a.contains(element);};
+
+	return std::find_if(intervals.begin(), intervals.end(), predicate)
+		!= intervals.end();
+}
+
+static Interval parse_interval(const std::string str) {
+	size_t minus = str.find("-");
+
+	int from, to;
+	try {
+		// only one int, not a range
+		if (minus == std::string::npos) {
+			from = to = std::stoi(str);
+		} else {
+			auto from_str = str.substr(0, minus);
+			auto to_str = str.substr(minus+1, str.length()-minus);
+
+			from = std::stoi(from_str);
+			to = std::stoi(to_str);
+		}
+	} catch (std::invalid_argument e) {
+		err() << "Invalid page range \"" << str << "\". "
+		      << "Expected a single page or a range PAGE1-PAGE2." << std::endl;
+		exit(EXIT_ERROR);
+	}
+
+	if (from <= 0 || to <= 0) {
+		err() << "Invalid page range \"" << str << "\". "
+		      << "Page numbers must be positive." << std::endl;
+		exit(EXIT_ERROR);
+	}
+
+	if (to < from) {
+		err() << "warning: Page range is empty: " << str << std::endl;
+	}
+
+	return Interval(from, to);
+}
+
+IntervalContainer IntervalContainer::fromString(const std::string str) {
+	IntervalContainer c;
+	std::stringstream tokens(str);
+
+	std::string interval;
+	while (std::getline(tokens, interval, ',')) {
+		c.addInterval(parse_interval(interval));
+	}
+
+	return c;
+}