Merge pull request #725 from cppalliance/128

Remove u128 x64 intrinsic pessimzations
cppalliance · Sep 19, 2024 · 7fe2e8f · 7fe2e8f
2 parents 693907f + c995e23
commit 7fe2e8f
Showing 1 changed file with 22 additions and 68 deletions.
diff --git a/include/boost/decimal/detail/emulated128.hpp b/include/boost/decimal/detail/emulated128.hpp
@@ -757,31 +757,15 @@ constexpr auto uint128::operator+=(std::uint64_t n) noexcept -> uint128&
 
 constexpr auto operator+(uint128 lhs, uint128 rhs) noexcept -> uint128
 {
-    #if (defined(BOOST_DECIMAL_HAS_X64_INTRINSICS) || defined(BOOST_DECIMAL_HAS_MSVC_64BIT_INTRINSICS)) && !defined(BOOST_DECIMAL_NO_CONSTEVAL_DETECTION)
-    if (!BOOST_DECIMAL_IS_CONSTANT_EVALUATED(lhs.low))
-    {
-        // Branchless version can be executed on x64 machines when available
-        unsigned long long low {};
-        unsigned long long high {};
-
-        const auto carry {BOOST_DECIMAL_ADD_CARRY(0, lhs.low, rhs.low, &low)};
-        BOOST_DECIMAL_ADD_CARRY(carry, lhs.high, rhs.high, &high);
+    uint128 temp {lhs.high + rhs.high, lhs.low + rhs.low};
 
-        return uint128{high, low};
-    }
-    else
-    #endif
+    // Need to carry a bit into rhs
+    if (temp.low < lhs.low)
     {
-        uint128 temp {lhs.high + rhs.high, lhs.low + rhs.low};
-
-        // Need to carry a bit into rhs
-        if (temp.low < lhs.low)
-        {
-            ++temp.high;
-        }
-
-        return temp;
+        ++temp.high;
     }
+
+    return temp;
 }
 
 constexpr auto uint128::operator+=(uint128 v) noexcept -> uint128&
@@ -807,31 +791,15 @@ constexpr auto uint128::operator++(int) noexcept -> uint128
 
 constexpr auto operator-(uint128 lhs, uint128 rhs) noexcept -> uint128
 {
-    #if (defined(BOOST_DECIMAL_HAS_X64_INTRINSICS) || defined(BOOST_DECIMAL_HAS_MSVC_64BIT_INTRINSICS)) && !defined(BOOST_DECIMAL_NO_CONSTEVAL_DETECTION)
-    if (!BOOST_DECIMAL_IS_CONSTANT_EVALUATED(lhs.low))
-    {
-        // Branchless version can be executed on x64 machines when available
-        unsigned long long low {};
-        unsigned long long high {};
-
-        const auto carry {_subborrow_u64(0, lhs.low, rhs.low, &low)};
-        _subborrow_u64(carry, lhs.high, rhs.high, &high);
+    uint128 temp {lhs.high - rhs.high, lhs.low - rhs.low};
 
-        return uint128{high, low};
-    }
-    else
-    #endif
+    // Check for carry
+    if (lhs.low < rhs.low)
     {
-        uint128 temp {lhs.high - rhs.high, lhs.low - rhs.low};
-
-        // Check for carry
-        if (lhs.low < rhs.low)
-        {
-            --temp.high;
-        }
-
-        return temp;
+        --temp.high;
     }
+
+    return temp;
 }
 
 constexpr auto uint128::operator-=(uint128 v) noexcept -> uint128&
@@ -1328,35 +1296,21 @@ constexpr auto int128::operator>(int rhs) const noexcept -> bool
 
 constexpr auto operator+(const int128& lhs, const int128& rhs) noexcept -> int128
 {
-    #if (defined(BOOST_DECIMAL_HAS_X64_INTRINSICS) || defined(BOOST_DECIMAL_HAS_MSVC_64BIT_INTRINSICS)) && !defined(BOOST_DECIMAL_NO_CONSTEVAL_DETECTION)
-    if (!BOOST_DECIMAL_IS_CONSTANT_EVALUATED(lhs.low))
-    {
-        unsigned long long low {};
-        unsigned long long high {};
-
-        const auto carry {BOOST_DECIMAL_ADD_CARRY(0, lhs.low, rhs.low, &low)};
-        BOOST_DECIMAL_ADD_CARRY(carry, static_cast<std::uint64_t>(lhs.high), static_cast<std::uint64_t>(rhs.high), &high);
-
-        return {static_cast<std::int64_t>(high), low};
-    }
-    #endif
-    {
-        #ifdef BOOST_DECIMAL_HAS_INT128
+    #ifdef BOOST_DECIMAL_HAS_INT128
 
-        const auto lhs_full {(static_cast<__uint128_t>(lhs.high) << 64) | lhs.low};
-        const auto rhs_full {(static_cast<__uint128_t>(rhs.high) << 64) | rhs.low};
-        const auto result {lhs_full + rhs_full};
+    const auto lhs_full {(static_cast<__uint128_t>(lhs.high) << 64) | lhs.low};
+    const auto rhs_full {(static_cast<__uint128_t>(rhs.high) << 64) | rhs.low};
+    const auto result {lhs_full + rhs_full};
 
-        return {static_cast<std::int64_t>(result >> 64), static_cast<std::uint64_t>(result)};
+    return {static_cast<std::int64_t>(result >> 64), static_cast<std::uint64_t>(result)};
 
-        #else
+    #else
 
-        const auto new_low {lhs.low + rhs.low};
-        const auto new_high {lhs.high + rhs.high + static_cast<std::int64_t>(new_low < lhs.low)};
-        return int128{new_high, new_low};
+    const auto new_low {lhs.low + rhs.low};
+    const auto new_high {lhs.high + rhs.high + static_cast<std::int64_t>(new_low < lhs.low)};
+    return int128{new_high, new_low};
 
-        #endif
-    }
+    #endif
 }
 
 constexpr auto operator-(const int128& lhs, const int128& rhs) noexcept -> int128