Move branchless functions to a dedicated file.

2026-08-03 02:18:31 +03:00
parent 2323020714
commit d2c5cf891d
2 changed files with 93 additions and 76 deletions
@@ -0,0 +1,86 @@
+#ifndef CHAOS_SERVICE_BRANCHLESS_HPP
+#define CHAOS_SERVICE_BRANCHLESS_HPP
+
+#include <type_traits>
+#include <climits>
+#include <cstdint>
+
+namespace Chaos::Service
+{
+
+struct Branchless
+{
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt Msb(InUInt in) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+
+        constexpr uint8_t shift = (sizeof(InUInt) * CHAR_BIT) - 1;
+        return static_cast<OutUInt>(0) - (in >> shift);
+    }
+
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt Lt(InUInt lhs, InUInt rhs) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+        static_assert(sizeof(InUInt) <= sizeof(uint64_t));
+
+        const uint64_t lhsEx = lhs;
+        const uint64_t rhsEx = rhs;
+
+        return Msb<OutUInt>(lhsEx ^ ((lhsEx ^ rhsEx) | ((lhsEx - rhsEx) ^ lhsEx)));
+    }
+
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt IsZero(InUInt in) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+        static_assert(sizeof(InUInt) <= sizeof(uint64_t));
+
+        const uint64_t inEx = in;
+
+        return Msb<OutUInt>(~inEx & (inEx - 1U));
+    }
+
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt Eq(InUInt lhs, InUInt rhs) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+
+        return IsZero<OutUInt, InUInt>(lhs ^ rhs);
+    }
+
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt Ge(InUInt lhs, InUInt rhs) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+
+        return ~Lt<OutUInt>(lhs, rhs);
+    }
+
+    template<typename OutUInt, typename InUInt>
+    static constexpr OutUInt Gt(InUInt lhs, InUInt rhs) noexcept
+    {
+        static_assert(std::is_unsigned_v<OutUInt> &&
+                      std::is_unsigned_v<InUInt>);
+
+        return Lt<OutUInt>(rhs, lhs);
+    }
+
+    template<typename UInt>
+    static constexpr UInt Sel(UInt mask, UInt onTrue, UInt onFalse) noexcept
+    {
+        static_assert(std::is_unsigned_v<UInt>);
+
+        return (mask & onTrue) | (~mask & onFalse);
+    }
+};
+
+} // namespace Chaos::Service
+
+#endif // CHAOS_SERVICE_BRANCHLESS_HPP