add our own endianness check because there is apparently no proper way to check for that at compile time

.gitignore

@@ -4,5 +4,9 @@
 /dependencies/*
 !/dependencies/.placeholder
 
+# ignore endianness check
+/.endianness
+/resources/check_endianness
+
 # ignore nano's temp files
 *.swp

resources/check_endianness.cpp

@@ -0,0 +1,66 @@
+// Copyright <year>, FOSS-VG Developers and Contributers
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, version 3.
+//
+// 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// version 3 along with this program.
+// If not, see https://www.gnu.org/licenses/agpl-3.0.en.html
+
+#include <iostream>
+#include <cstdint>
+
+int main() {
+    uint32_t* testInteger = new uint32_t;
+    *testInteger = 0x04030201;
+    auto data = reinterpret_cast<std::uint8_t*>(testInteger);
+
+    if (
+        *data  ==  0x01 &&
+        *(data+1)==0x02 &&
+        *(data+2)==0x03 &&
+        *(data+3)==0x04
+    ) {
+        std::cerr << "Little Endian" << std::endl;
+        std::cout << "#define FOSSVG_LITTLE_ENDIAN" << std::endl;
+    } else if (
+        *data  ==  0x04 &&
+        *(data+1)==0x03 &&
+        *(data+2)==0x02 &&
+        *(data+3)==0x01
+    ) {
+        std::cerr << "Big Endian" << std::endl;
+        std::cout << "#define FOSSVG_BIG_ENDIAN" << std::endl;
+    } else if (
+        *data  ==  0x03 &&
+        *(data+1)==0x04 &&
+        *(data+2)==0x01 &&
+        *(data+3)==0x02
+    ) {
+        std::cerr << "PDP Endian (Little Word)" << std::endl;
+        std::cout << "#define FOSSVG_ENDIAN_LITTLE_WORD /* PDP-11-style byte-swapped words */" << std::endl;
+    } else if (
+        *data  ==  0x02 &&
+        *(data+1)==0x01 &&
+        *(data+2)==0x04 &&
+        *(data+3)==0x03
+    ) {
+        std::cerr << "Honeywell Endian (Big Word)" << std::endl;
+        std::cout << "#define FOSSVG_ENDIAN_BIG_WORD /* Honeywell-316-style byte-swapped words */" << std::endl;
+
+    } else {
+        std::cerr << "Unknown Endianness" << std::endl;
+        std::cout << "#define FOSSVG_ENDIAN_UNKNOWN" << std::endl;
+    }
+
+    delete data;
+
+    std::cerr << "WARNING: This test may be unreliable. If you encounter issues, check the endianness of your machine and set it manually. Bi-endianness is not supported." << std::endl;
+    return 0;
+}

scripts/build.sh

@@ -23,6 +23,20 @@ if [ -z "$CXXFLAGS" ]; then
 fi
 CXX_WITH_FLAGS="$CXX $CXXFLAGS"
 
+# if unknown, figure out endianness
+if [ -f .endianness ]; then
+    echo "Endianness known:"
+    cat .endianness
+else
+    echo "Endianness unknown."
+    if [ ! -x resources/check_endianness ]; then
+        echo "Building endianness test."
+        $CXX_WITH_FLAGS -o resources/check_endianness resources/check_endianness.cpp
+    fi
+    echo "Probing endianness:"
+    resources/check_endianness > .endianness
+fi
+
 # `.cpp` files in src/lib will be automatically picked up and compiled into
 # dynamically linked libraries.
 echo "Building libs..."

scripts/clean.sh

@@ -16,6 +16,8 @@
 # If not, see https://www.gnu.org/licenses/agpl-3.0.en.html
 
 rm -rv ./bin
+rm -vf .endianness
+rm -vf resources/check_endianness
 mkdir -v ./bin
 set -v
 echo -n "" > ./bin/.placeholder