From 23234f1a360f9f9c930fd5bbd7901fd0ca00871e Mon Sep 17 00:00:00 2001
From: Gard Spreemann <gard.spreemann@epfl.ch>
Date: Wed, 30 Oct 2019 18:11:21 +0100
Subject: Endian-safety on big endian architectures.

---
 README.md  |  3 ++-
 ripser.cpp | 33 +++++++++++++++++++++++++--------
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 2ce826f..ca98030 100644
--- a/README.md
+++ b/README.md
@@ -62,6 +62,7 @@ Ripser supports several compile-time options. They are switched on by defining t
   - `INDICATE_PROGRESS`: indicate the current progress in the console
   - `PRINT_PERSISTENCE_PAIRS`: output the computed persistence pairs (enabled by default in the code; comment out to disable)
   - `USE_GOOGLE_HASHMAP`: enable support for Google's [sparsehash] data structure; may further reduce memory footprint
+  - `BIGENDIAN`: build for running on a big endian architecture
 
 For example, to build Ripser with support for Google's hashmap:
 
@@ -128,4 +129,4 @@ Ripser is licensed under the [MIT] license (`COPYING.txt`), with an extra clause
 [Perseus]: <http://www.sas.upenn.edu/~vnanda/perseus/>
 [GUDHI]: <http://gudhi.gforge.inria.fr>
 [sparsehash]: <https://github.com/sparsehash/sparsehash>
-[MIT]: <https://opensource.org/licenses/mit-license.php>
\ No newline at end of file
+[MIT]: <https://opensource.org/licenses/mit-license.php>
diff --git a/ripser.cpp b/ripser.cpp
index 1ae62e1..f420f2a 100644
--- a/ripser.cpp
+++ b/ripser.cpp
@@ -830,10 +830,27 @@ enum file_format {
 	BINARY
 };
 
-template <typename T> T read(std::istream& input_stream) {
+template <typename T> inline void reverse_endianness(T& x) {
+	uint8_t* p = reinterpret_cast<uint8_t *>(&x);
+	std::reverse(p, p + sizeof(T));
+}
+
+template <typename T> T read_le(std::istream& input_stream) {
+	T result;
+	input_stream.read(reinterpret_cast<char*>(&result), sizeof(T));
+	#ifdef BIGENDIAN
+	reverse_endianness(result);
+	#endif
+	return result;
+}
+
+template <typename T> T read_be(std::istream& input_stream) {
 	T result;
 	input_stream.read(reinterpret_cast<char*>(&result), sizeof(T));
-	return result; // on little endian: boost::endian::little_to_native(result);
+	#ifndef BIGENDIAN
+	reverse_endianness(result);
+	#endif
+	return result;
 }
 
 compressed_lower_distance_matrix read_point_cloud(std::istream& input_stream) {
@@ -929,33 +946,33 @@ compressed_lower_distance_matrix read_distance_matrix(std::istream& input_stream
 }
 
 compressed_lower_distance_matrix read_dipha(std::istream& input_stream) {
-	if (read<int64_t>(input_stream) != 8067171840) {
+	if (read_le<int64_t>(input_stream) != 8067171840) {
 		std::cerr << "input is not a Dipha file (magic number: 8067171840)" << std::endl;
 		exit(-1);
 	}
 
-	if (read<int64_t>(input_stream) != 7) {
+	if (read_le<int64_t>(input_stream) != 7) {
 		std::cerr << "input is not a Dipha distance matrix (file type: 7)" << std::endl;
 		exit(-1);
 	}
 
-	index_t n = read<int64_t>(input_stream);
+	index_t n = read_le<int64_t>(input_stream);
 
 	std::vector<value_t> distances;
 
 	for (int i = 0; i < n; ++i)
 		for (int j = 0; j < n; ++j)
 			if (i > j)
-				distances.push_back(read<double>(input_stream));
+				distances.push_back(read_le<double>(input_stream));
 			else
-				read<double>(input_stream);
+				read_le<double>(input_stream);
 
 	return compressed_lower_distance_matrix(std::move(distances));
 }
 
 compressed_lower_distance_matrix read_binary(std::istream& input_stream) {
 	std::vector<value_t> distances;
-	while (!input_stream.eof()) distances.push_back(read<value_t>(input_stream));
+	while (!input_stream.eof()) distances.push_back(read_le<value_t>(input_stream));
 	return compressed_lower_distance_matrix(std::move(distances));
 }
 
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