From 59d71b242341a0f2bb56c19709d634a995ecd675 Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Sun, 5 Feb 2023 11:32:14 +0000
Subject: [PATCH] introducing binary safe type cast utility.

---
 Sources/Core/Math.h              | 16 ++++++++++++++++
 Sources/Core/OpusAudioStream.cpp |  8 ++++----
 Sources/Core/SdlFileStream.cpp   |  5 +++--
 Sources/Draw/SWImageRenderer.cpp |  4 ++--
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/Sources/Core/Math.h b/Sources/Core/Math.h
index da968ebb7..1b1eb7e8a 100644
--- a/Sources/Core/Math.h
+++ b/Sources/Core/Math.h
@@ -23,10 +23,12 @@
 #include <algorithm> // std::max / std::min
 #include <cstdint>   // uint32_t --> msvc
 #include <cmath>
+#include <cstring>
 #include <random>
 #include <string>
 #include <vector>
 #include <functional>
+#include <type_traits>
 #include <mutex>
 
 namespace spades {
@@ -973,6 +975,20 @@ namespace spades {
 	std::string TrimSpaces(const std::string &);
 
 	float SmoothStep(float);
+
+    /*
+     * binary safe cast, unlike traditional c++ cast operators, it needs to operate on a matching type size
+     *
+     * if the code updates to c++ 20 it can be dropped
+     */
+    template<bool dest, class src> using EnableIf = typename std::enable_if<dest, src>::type;
+    template<class dest, class src>
+    EnableIf<sizeof(dest) == sizeof(src) && std::is_trivially_copyable<dest>::value && std::is_trivially_copyable<src>::value, dest>
+    SafeCast(const src& s) {
+        dest d;
+        std::memcpy(&d, &s, sizeof(dest));
+        return d;
+    }
 }
 
 namespace std {
diff --git a/Sources/Core/OpusAudioStream.cpp b/Sources/Core/OpusAudioStream.cpp
index 751d1fc37..517660be4 100644
--- a/Sources/Core/OpusAudioStream.cpp
+++ b/Sources/Core/OpusAudioStream.cpp
@@ -69,19 +69,19 @@ namespace spades {
 			switch (whence) {
 				case SEEK_CUR:
 					self.stream->SetPosition(
-					  static_cast<std::uint64_t>(offset + self.stream->GetPosition()));
+					  SafeCast<std::uint64_t>(offset + self.stream->GetPosition()));
 					break;
 				case SEEK_SET: self.stream->SetPosition(static_cast<std::uint64_t>(offset)); break;
 				case SEEK_END:
 					self.stream->SetPosition(
-					  static_cast<std::uint64_t>(offset + self.stream->GetLength()));
+					  SafeCast<std::uint64_t>(offset + self.stream->GetLength()));
 					break;
 			}
 			return 0;
 		};
 		opusCallback->tell = [](void *stream) -> opus_int64 {
 			auto &self = *reinterpret_cast<OpusAudioStream *>(stream);
-			return static_cast<opus_int64>(self.stream->GetPosition());
+			return SafeCast<opus_int64>(self.stream->GetPosition());
 		};
 		opusCallback->close = nullptr;
 
@@ -220,7 +220,7 @@ namespace spades {
 	void OpusAudioStream::SetPosition(uint64_t pos) {
 		pos = std::min(pos, GetLength());
 
-		op_pcm_seek(opusFile, static_cast<opus_int64>(pos / (channels * 4)));
+		op_pcm_seek(opusFile, SafeCast<opus_int64>(pos / (channels * 4)));
 
 		subsamplePosition = static_cast<int>(pos % (channels * 4));
 		if (subsamplePosition) {
diff --git a/Sources/Core/SdlFileStream.cpp b/Sources/Core/SdlFileStream.cpp
index 21cab1f6f..26b329034 100644
--- a/Sources/Core/SdlFileStream.cpp
+++ b/Sources/Core/SdlFileStream.cpp
@@ -21,6 +21,7 @@
 #include "SdlFileStream.h"
 #include "Debug.h"
 #include "Exception.h"
+#include "Math.h"
 
 namespace spades {
 	SdlFileStream::SdlFileStream(SDL_RWops *f, bool ac) : ops(f), autoClose(ac) {
@@ -76,7 +77,7 @@ namespace spades {
 		if (pos == -1) {
 			SPRaise("This stream doesn't support seeking.");
 		}
-		return static_cast<uint64_t>(pos);
+		return SafeCast<uint64_t>(pos);
 	}
 
 	void SdlFileStream::SetPosition(uint64_t pos) {
@@ -86,7 +87,7 @@ namespace spades {
 			SPRaise("Currently SdlFileStream doesn't support 64-bit offset.");
 		}
 
-		if (SDL_RWseek(ops, static_cast<Sint64>(pos), RW_SEEK_SET) == -1) {
+		if (SDL_RWseek(ops, SafeCast<Sint64>(pos), RW_SEEK_SET) == -1) {
 			SPRaise("This stream doesn't support seeking.");
 		}
 	}
diff --git a/Sources/Draw/SWImageRenderer.cpp b/Sources/Draw/SWImageRenderer.cpp
index d46e45d0d..702f2290e 100644
--- a/Sources/Draw/SWImageRenderer.cpp
+++ b/Sources/Draw/SWImageRenderer.cpp
@@ -78,10 +78,10 @@ namespace spades {
 					}
 					if (numSteps == 0)
 						numSteps = 1;
-					b.divisor = static_cast<unsigned int>(numSteps);
+					b.divisor = SafeCast<unsigned int>(numSteps);
 					b.dividend = 0;
 					b.largePos = start;
-					b.step = static_cast<unsigned int>(distance);
+					b.step = SafeCast<unsigned int>(distance);
 				} else {
 					mode = 0;
 					if (numSteps == 0) {