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GH-44767: [C++] Fix Float16.To{Little,Big}Endian on big endian machines #44768

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merged 1 commit into from
Nov 18, 2024
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GH-44767: [C++] Fix Float16.To{Little,Big}Endian on big endian machines #44768

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8 changes: 0 additions & 8 deletions cpp/src/arrow/util/float16.h
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Original file line number Diff line number Diff line change
Expand Up @@ -111,11 +111,7 @@ class ARROW_EXPORT Float16 {
}
/// \brief Return the value's bytes in little-endian byte order
constexpr std::array<uint8_t, 2> ToLittleEndian() const {
#if ARROW_LITTLE_ENDIAN
return {uint8_t(bits_ & 0xff), uint8_t(bits_ >> 8)};
#else
return {uint8_t(bits_ >> 8), uint8_t(bits_ & 0xff)};
#endif
}

/// \brief Copy the value's bytes in big-endian byte order
Expand All @@ -125,11 +121,7 @@ class ARROW_EXPORT Float16 {
}
/// \brief Return the value's bytes in big-endian byte order
constexpr std::array<uint8_t, 2> ToBigEndian() const {
#if ARROW_LITTLE_ENDIAN
return {uint8_t(bits_ >> 8), uint8_t(bits_ & 0xff)};
#else
return {uint8_t(bits_ & 0xff), uint8_t(bits_ >> 8)};
#endif
}

constexpr Float16 operator-() const { return FromBits(bits_ ^ 0x8000); }
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47 changes: 28 additions & 19 deletions cpp/src/arrow/util/float16_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -323,44 +323,53 @@ TEST(Float16Test, Compare) {
TEST(Float16Test, ToBytes) {
constexpr auto f16 = Float16::FromBits(0xd01c);
std::array<uint8_t, 2> bytes;
auto load = [&bytes]() { return SafeLoadAs<uint16_t>(bytes.data()); };

constexpr uint8_t expected_high = 0xd0;
constexpr uint8_t expected_low = 0x1c;

// Test native-endian
f16.ToBytes(bytes.data());
ASSERT_EQ(load(), 0xd01c);
#if ARROW_LITTLE_ENDIAN
ASSERT_EQ(bytes[0], expected_low);
ASSERT_EQ(bytes[1], expected_high);
#else
ASSERT_EQ(bytes[0], expected_high);
ASSERT_EQ(bytes[1], expected_low);
#endif
bytes = f16.ToBytes();
ASSERT_EQ(load(), 0xd01c);

#if ARROW_LITTLE_ENDIAN
constexpr uint16_t expected_le = 0xd01c;
constexpr uint16_t expected_be = 0x1cd0;
ASSERT_EQ(bytes[0], expected_low);
ASSERT_EQ(bytes[1], expected_high);
#else
constexpr uint16_t expected_le = 0x1cd0;
constexpr uint16_t expected_be = 0xd01c;
ASSERT_EQ(bytes[0], expected_high);
ASSERT_EQ(bytes[1], expected_low);
#endif

// Test little-endian
f16.ToLittleEndian(bytes.data());
ASSERT_EQ(load(), expected_le);
ASSERT_EQ(bytes[0], expected_low);
ASSERT_EQ(bytes[1], expected_high);
bytes = f16.ToLittleEndian();
ASSERT_EQ(load(), expected_le);
ASSERT_EQ(bytes[0], expected_low);
ASSERT_EQ(bytes[1], expected_high);
// Test big-endian
f16.ToBigEndian(bytes.data());
ASSERT_EQ(load(), expected_be);
ASSERT_EQ(bytes[0], expected_high);
ASSERT_EQ(bytes[1], expected_low);
bytes = f16.ToBigEndian();
ASSERT_EQ(load(), expected_be);
ASSERT_EQ(bytes[0], expected_high);
ASSERT_EQ(bytes[1], expected_low);
}

TEST(Float16Test, FromBytes) {
constexpr uint16_t u16 = 0xd01c;
const auto* data = reinterpret_cast<const uint8_t*>(&u16);
ASSERT_EQ(Float16::FromBytes(data), Float16::FromBits(0xd01c));
const std::array<uint8_t, 2> bytes = {0x1c, 0xd0};
#if ARROW_LITTLE_ENDIAN
ASSERT_EQ(Float16::FromLittleEndian(data), Float16::FromBits(0xd01c));
ASSERT_EQ(Float16::FromBigEndian(data), Float16::FromBits(0x1cd0));
ASSERT_EQ(Float16::FromBytes(bytes.data()), Float16::FromBits(0xd01c));
#else
ASSERT_EQ(Float16::FromLittleEndian(data), Float16(0x1cd0));
ASSERT_EQ(Float16::FromBigEndian(data), Float16(0xd01c));
ASSERT_EQ(Float16::FromBytes(bytes.data()), Float16::FromBits(0x1cd0));
#endif
ASSERT_EQ(Float16::FromLittleEndian(bytes.data()), Float16::FromBits(0xd01c));
ASSERT_EQ(Float16::FromBigEndian(bytes.data()), Float16::FromBits(0x1cd0));
}

} // namespace
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