xref: /llvm-project/libc/src/__support/FPUtil/generic/mul.h (revision 74a1ca504bf60f02431140ee72dbe1c158556237)

//===-- Multiplication of IEEE 754 floating-point numbers -------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SRC___SUPPORT_FPUTIL_GENERIC_MUL_H
#define LLVM_LIBC_SRC___SUPPORT_FPUTIL_GENERIC_MUL_H

#include "hdr/errno_macros.h"
#include "hdr/fenv_macros.h"
#include "src/__support/CPP/bit.h"
#include "src/__support/CPP/type_traits.h"
#include "src/__support/FPUtil/BasicOperations.h"
#include "src/__support/FPUtil/FEnvImpl.h"
#include "src/__support/FPUtil/FPBits.h"
#include "src/__support/FPUtil/dyadic_float.h"
#include "src/__support/macros/attributes.h"
#include "src/__support/macros/config.h"
#include "src/__support/macros/optimization.h"

namespace LIBC_NAMESPACE_DECL {
namespace fputil::generic {

template <typename OutType, typename InType>
LIBC_INLINE cpp::enable_if_t<cpp::is_floating_point_v<OutType> &&
                                 cpp::is_floating_point_v<InType> &&
                                 sizeof(OutType) <= sizeof(InType),
                             OutType>
mul(InType x, InType y) {
  using OutFPBits = FPBits<OutType>;
  using OutStorageType = typename OutFPBits::StorageType;
  using InFPBits = FPBits<InType>;
  using InStorageType = typename InFPBits::StorageType;
  // The product of two p-digit numbers is a 2p-digit number.
  using DyadicFloat =
      DyadicFloat<cpp::bit_ceil(2 * static_cast<size_t>(InFPBits::SIG_LEN))>;

  InFPBits x_bits(x);
  InFPBits y_bits(y);

  Sign result_sign = x_bits.sign() == y_bits.sign() ? Sign::POS : Sign::NEG;

  if (LIBC_UNLIKELY(x_bits.is_inf_or_nan() || y_bits.is_inf_or_nan() ||
                    x_bits.is_zero() || y_bits.is_zero())) {
    if (x_bits.is_nan() || y_bits.is_nan()) {
      if (x_bits.is_signaling_nan() || y_bits.is_signaling_nan())
        raise_except_if_required(FE_INVALID);

      if (x_bits.is_quiet_nan()) {
        InStorageType x_payload = x_bits.get_mantissa();
        x_payload >>= InFPBits::FRACTION_LEN - OutFPBits::FRACTION_LEN;
        return OutFPBits::quiet_nan(x_bits.sign(),
                                    static_cast<OutStorageType>(x_payload))
            .get_val();
      }

      if (y_bits.is_quiet_nan()) {
        InStorageType y_payload = y_bits.get_mantissa();
        y_payload >>= InFPBits::FRACTION_LEN - OutFPBits::FRACTION_LEN;
        return OutFPBits::quiet_nan(y_bits.sign(),
                                    static_cast<OutStorageType>(y_payload))
            .get_val();
      }

      return OutFPBits::quiet_nan().get_val();
    }

    if (x_bits.is_inf()) {
      if (y_bits.is_zero()) {
        set_errno_if_required(EDOM);
        raise_except_if_required(FE_INVALID);
        return OutFPBits::quiet_nan().get_val();
      }

      return OutFPBits::inf(result_sign).get_val();
    }

    if (y_bits.is_inf()) {
      if (x_bits.is_zero()) {
        set_errno_if_required(EDOM);
        raise_except_if_required(FE_INVALID);
        return OutFPBits::quiet_nan().get_val();
      }

      return OutFPBits::inf(result_sign).get_val();
    }

    // Now either x or y is zero, and the other one is finite.
    return OutFPBits::zero(result_sign).get_val();
  }

  DyadicFloat xd(x);
  DyadicFloat yd(y);

  DyadicFloat result = quick_mul(xd, yd);
  return result.template as<OutType, /*ShouldSignalExceptions=*/true>();
}

} // namespace fputil::generic
} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_FPUTIL_GENERIC_MUL_H