FEX-Emu--FEX/FEXCore/include/FEXCore/Utils/FPState.h

// SPDX-License-Identifier: MIT
#pragma once

#include <cstdint>

namespace FEXCore::FPState {
enum class X87Tag : uint8_t { Valid = 0b00, Zero = 0b01, Special = 0b10, Empty = 0b11 };

static inline X87Tag GetX87Tag(uint64_t (&Reg)[2], bool Valid) {
  if (!Valid) {
    return X87Tag::Empty;
  }

  const uint64_t Exponent = Reg[1] & 0x7fff;
  if (Exponent == 0x7fff) {
    // (Pseudo) NaN / Inf
    return X87Tag::Special;
  }

  const bool JBit = Reg[0] & (1ULL << 63);
  if (Exponent == 0) {
    const uint64_t Fraction = Reg[0] & ((1ULL << 63) - 1);
    if (!JBit && !Fraction) {
      return X87Tag::Zero;
    } else {
      // (Pseudo) Subnormal
      return X87Tag::Special;
    }
  }

  if (JBit) {
    // Normal
    return X87Tag::Valid;
  } else {
    // Invalid
    return X87Tag::Special;
  }
}

static inline uint16_t ConvertFromAbridgedFTW(uint16_t FSW, uint64_t (&MM)[8][2], uint8_t AbridgedFTW) {
  const uint32_t StackTop = (FSW >> 11) & 0b111;

  uint16_t FTW = 0;
  for (uint32_t i = 0; i < 8; i++) {
    // The AMD manually incorrectly states there is a direct mapping here, only the intel-manual correctly states
    // the stack-relative behaviour
    const uint16_t StackIndex = (i - StackTop) & 0b111;
    const X87Tag Tag = GetX87Tag(MM[StackIndex], AbridgedFTW & (1 << i));
    FTW |= static_cast<uint8_t>(Tag) << (2 * i);
  }

  return FTW;
}

static inline uint8_t ConvertToAbridgedFTW(uint16_t FTW) {
  uint8_t AbridgedFTW = 0;

  for (uint32_t i = 0; i < 8; i++) {
    const X87Tag Tag = static_cast<X87Tag>((FTW >> (2 * i)) & 3);
    AbridgedFTW |= ((Tag == X87Tag::Empty) ? 0 : 1) << i;
  }

  return AbridgedFTW;
}
} // namespace FEXCore::FPState