libc/src/__support/math/tanbf16.h

//===-- Implementation of tanbf16 function --------------------------------===//
//
// 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_MATH_TANBF16_H
#define LLVM_LIBC_SRC___SUPPORT_MATH_TANBF16_H

#include "hdr/errno_macros.h"
#include "hdr/fenv_macros.h"
#include "sincosf_utils.h"
#include "src/__support/FPUtil/FEnvImpl.h"
#include "src/__support/FPUtil/FPBits.h"
#include "src/__support/FPUtil/bfloat16.h"
#include "src/__support/FPUtil/cast.h"
#include "src/__support/FPUtil/multiply_add.h"
#include "src/__support/macros/optimization.h"

namespace LIBC_NAMESPACE_DECL {

namespace math {

LIBC_INLINE bfloat16 tanbf16(bfloat16 x) {

  using FPBits = fputil::FPBits<bfloat16>;
  FPBits xbits(x);

  uint16_t x_u = xbits.uintval();
  uint16_t x_abs = x_u & 0x7fff;
  float xf = x;

  // NaN or -/+ INF
  if (x_abs >= 0x7F80) {
    // NaN
    if (xbits.is_nan()) {
      if (xbits.is_signaling_nan()) {
        fputil::raise_except_if_required(FE_INVALID);
        return FPBits::quiet_nan().get_val();
      }
      return x;
    }
    //|x| is +/- INF
    fputil::set_errno_if_required(EDOM);
    fputil::raise_except_if_required(FE_INVALID);
    return x + FPBits::quiet_nan().get_val();
  }

  // Through Exhaustive testing -
  // The last value where tan(x) ~ x is 0x3db8
  if (LIBC_UNLIKELY(x_abs <= 0x3db8)) {
    // |x| = {0}
    if (LIBC_UNLIKELY(x_abs == 0)) {
      return x;
    }
    return fputil::cast<bfloat16>(fputil::multiply_add(xf, 0x1.0p-11f, xf));
  }

  double xd = static_cast<double>(xf);
  uint32_t x_abs_f = fputil::FPBits<float>(xf).uintval() & 0x7fffffff;
  double sin_k, cos_k, sin_y, cosm1_y;

  // TODO: Use bfloat16 version for inv_trigf_utils_internals after they are
  // available
  // Tracking issue :
  // https://github.com/llvm/llvm-project/issues/202079
  sincosf_utils_internal::sincosf_eval(xd, x_abs_f, sin_k, cos_k, sin_y,
                                       cosm1_y);

  return fputil::cast<bfloat16>(
      fputil::multiply_add(sin_y, cos_k,
                           fputil::multiply_add(cosm1_y, sin_k, sin_k)) /
      fputil::multiply_add(sin_y, -sin_k,
                           fputil::multiply_add(cosm1_y, cos_k, cos_k)));
}

} // namespace math

} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_MATH_TANBF16_H