From 31421d5cc35541aea61767d544986a31e276db8e Mon Sep 17 00:00:00 2001
From: MikeGitb <MikeGitb@users.noreply.github.com>
Date: Sun, 18 Sep 2016 22:32:56 +0200
Subject: [PATCH] Add alternative implementations of gsl::byte

---
 gsl/gsl_byte               | 160 +++++++++++++++++++++++++++++++++++++
 tests/byte_tests.cpp       |  43 ++++++++--
 tests/multi_span_tests.cpp |   2 +-
 3 files changed, 199 insertions(+), 6 deletions(-)

diff --git a/gsl/gsl_byte b/gsl/gsl_byte
index 3f77923..90885f9 100644
--- a/gsl/gsl_byte
+++ b/gsl/gsl_byte
@@ -41,8 +41,167 @@
 
 #endif // _MSC_VER
 
+#define GSL_BYTE_TYPE_ENUM 0
+#define GSL_BYTE_TYPE_UCHAR 1
+#define GSL_BYTE_TYPE_STRUCT 2
+
+#ifndef GSL_USE_BYTE_TYPE
+// currently clang++ as well as g++ don't allow a pointer to
+//
+// < enum class byte : unsigned char >
+//
+// to alias other types.
+// so we have to use a typedef to unsigned char instead.
+#ifdef _MSC_VER
+    #define GSL_USE_BYTE_TYPE GSL_BYTE_TYPE_ENUM
+#else
+    #define GSL_USE_BYTE_TYPE GSL_BYTE_TYPE_STRUCT
+#endif
+
+#endif
+
 namespace gsl
 {
+//################################### implemet byte as unsigned char ####################################
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+
+using byte = unsigned char;
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr IntegerType to_integer(byte b) noexcept
+{
+    return{ b };
+}
+
+template<bool E, typename T>
+inline constexpr byte to_byte_impl(T t) noexcept
+{
+    static_assert(
+        E,
+        "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
+        "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version."
+        );
+    return static_cast<byte>(t);
+}
+
+template<>
+inline constexpr byte to_byte_impl<true, unsigned char>(unsigned char t) noexcept
+{
+    return byte(t);
+}
+
+template<typename T>
+inline constexpr byte to_byte(T t) noexcept
+{
+    return to_byte_impl<std::is_same<T, unsigned char>::value, T>(t);
+}
+
+template <int I>
+inline constexpr byte to_byte() noexcept
+{
+    static_assert(I >= 0 && I <= 255, "gsl::byte only has 8 bits of storage, values must be in range 0-255");
+    return static_cast<byte>(I);
+}
+
+//################################### implemet byte as struct ####################################
+
+#elif GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_STRUCT
+
+// This is a simple definition for now that allows
+// use of byte within span<> to be standards-compliant
+struct byte {
+    unsigned char v;
+    explicit operator unsigned char&() { return v; }
+    explicit operator const unsigned char&() const { return v; }
+    friend bool operator==(byte l, byte r) { return l.v == r.v; }
+    friend bool operator!=(byte l, byte r) { return l.v != r.v; }
+};
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept
+{
+    return b.v <<= shift, b;
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte operator<<(byte b, IntegerType shift) noexcept
+{
+    return byte{ static_cast<unsigned char>(b.v << shift) };
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept
+{
+    return b.v >>= shift, b;
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr byte operator >> (byte b, IntegerType shift) noexcept
+{
+    return byte{ static_cast<unsigned char>(b.v >> shift) };
+}
+
+inline constexpr byte& operator|=(byte& l, byte r) noexcept
+{
+    return  l.v |= r.v, l;
+}
+
+inline constexpr byte operator|(byte l, byte r) noexcept
+{
+    return byte{ static_cast<unsigned char>(l.v | r.v) };
+}
+
+inline constexpr byte& operator&=(byte& l, byte r) noexcept
+{
+    return  l.v &= r.v, l;
+}
+
+inline constexpr byte operator&(byte l, byte r) noexcept
+{
+    return byte{ static_cast<unsigned char>(l.v & r.v) };
+}
+
+inline constexpr byte& operator^=(byte& l, byte r) noexcept
+{
+    return  l.v ^= r.v, l;
+}
+
+inline constexpr byte operator^(byte l, byte r) noexcept
+{
+    return byte{ static_cast<unsigned char>(l.v ^ r.v) };
+}
+
+inline constexpr byte operator~(byte b) noexcept { return byte{ static_cast<unsigned char>(~b.v) }; }
+
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+inline constexpr IntegerType to_integer(byte b) noexcept
+{
+    return static_cast<IntegerType>(b.v);
+}
+
+template<typename T>
+inline constexpr byte to_byte(T t) noexcept
+{
+    static_assert(
+        std::is_same<T, unsigned char>::value,
+        "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
+        "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version."
+        );
+    return byte{ t };
+}
+
+template <int I>
+inline constexpr byte to_byte() noexcept
+{
+    static_assert(I >= 0 && I <= 255, "gsl::byte only has 8 bits of storage, values must be in range 0-255");
+    return byte{ static_cast<unsigned char>(I) };
+}
+
+//################################### implemet byte as enum ####################################
+
+#elif GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_ENUM
+
 // This is a simple definition for now that allows
 // use of byte within span<> to be standards-compliant
 enum class byte : unsigned char
@@ -139,6 +298,7 @@ inline constexpr byte to_byte() noexcept
     static_assert(I >= 0 && I <= 255, "gsl::byte only has 8 bits of storage, values must be in range 0-255");
     return static_cast<byte>(I);
 }
+#endif // GSL_USE_ENUM_BYTE
 
 } // namespace gsl
 
diff --git a/tests/byte_tests.cpp b/tests/byte_tests.cpp
index 32b0957..4d52166 100644
--- a/tests/byte_tests.cpp
+++ b/tests/byte_tests.cpp
@@ -34,6 +34,17 @@ SUITE(byte_tests)
 {
     TEST(construction)
     {
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_STRUCT
+        {
+            byte b{ 4 };
+            CHECK(static_cast<unsigned char>(b) == 4);
+        }
+
+        {
+            byte b = byte{ 12 };
+            CHECK(static_cast<unsigned char>(b) == 12);
+        }
+#else
         {
             byte b = static_cast<byte>(4);
             CHECK(static_cast<unsigned char>(b) == 4);
@@ -43,6 +54,7 @@ SUITE(byte_tests)
             byte b = byte(12);
             CHECK(static_cast<unsigned char>(b) == 12);
         }
+#endif
 
         {
             byte b = to_byte<12>();
@@ -70,7 +82,7 @@ SUITE(byte_tests)
 
     TEST(aliasing)
     {
-        int i{0};
+        int i{ 0 };
         int res = modify_both(reinterpret_cast<byte*>(&i), &i);
         CHECK(res == i);
     }
@@ -78,32 +90,55 @@ SUITE(byte_tests)
     TEST(bitwise_operations)
     {
         byte b = to_byte<0xFF>();
-
         byte a = to_byte<0x00>();
+
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+        CHECK(static_cast<byte>(b | a) == to_byte<0xFF>());
+#else
         CHECK((b | a) == to_byte<0xFF>());
+#endif
+
         CHECK(a == to_byte<0x00>());
 
         a |= b;
         CHECK(a == to_byte<0xFF>());
 
         a = to_byte<0x01>();
+
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+        CHECK(static_cast<byte>(b & a) == to_byte<0x01>());
+#else
         CHECK((b & a) == to_byte<0x01>());
+#endif
 
         a &= b;
         CHECK(a == to_byte<0x01>());
 
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+        CHECK(static_cast<byte>(b ^ a) == to_byte<0xFE>());
+#else
         CHECK((b ^ a) == to_byte<0xFE>());
-        
+#endif
         CHECK(a == to_byte<0x01>());
+
         a ^= b;
         CHECK(a == to_byte<0xFE>());
 
         a = to_byte<0x01>();
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+        CHECK(static_cast<byte>(~a) == to_byte<0xFE>());
+#else
         CHECK(~a == to_byte<0xFE>());
+#endif
 
         a = to_byte<0xFF>();
+#if GSL_USE_BYTE_TYPE == GSL_BYTE_TYPE_UCHAR
+        CHECK(static_cast<byte>(a << 4) == to_byte<0xF0>());
+        CHECK(static_cast<byte>(a >> 4) == to_byte<0x0F>());
+#else
         CHECK((a << 4) == to_byte<0xF0>());
         CHECK((a >> 4) == to_byte<0x0F>());
+#endif
 
         a <<= 4;
         CHECK(a == to_byte<0xF0>());
@@ -129,7 +164,5 @@ SUITE(byte_tests)
 //      CHECK(0x12 == gsl::to_integer<double>(b));  // expect compile-time error
     }
 }
-
 }
-
 int main(int, const char* []) { return UnitTest::RunAllTests(); }
diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
index c0240ea..4e00e49 100644
--- a/tests/multi_span_tests.cpp
+++ b/tests/multi_span_tests.cpp
@@ -1663,7 +1663,7 @@ SUITE(multi_span_tests)
             multi_span<int, dynamic_range> av = a;
             auto wav = as_writeable_bytes(av);
             for (auto& b : wav) {
-                b = byte(0);
+                b = to_byte<0>();
             }
             for (size_t i = 0; i < 4; ++i) {
                 CHECK(a[i] == 0);