softrvv/include/softrvv_internal.h

/*
 * Copyright 2023 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SOFTRVV_INTERNAL_H
#define SOFTRVV_INTERNAL_H

#include <bit>
#include <tuple>

namespace softrvv {

template <typename T>
inline  std::tuple<int, int>get_element_and_pos(unsigned int index) {
  // bw_required is the number of bits required to store the value
  const unsigned int bw_required = std::__bit_width(sizeof(T)* 8);
  const unsigned int shift = bw_required - 1;
  // shift is the number of bits required to store the value minus 1
  // Example for T is int32_t:
  // 32 requires 6 bits to store, the shift required to divide by 32 is 5 (6 - 1)
  // Shift of the index is equivalent to a divide
  unsigned int element_idx = index >> shift;
  // Masked lowers bits are equivalent to remainder
  unsigned int element_pos = index & ~(element_idx << shift);
  return std::make_tuple(element_idx, element_pos);
}

template <typename T>
inline void set_bit_in_dest_mask(unsigned int index, T *dest, bool set_bit) {
  unsigned int element_idx;
  unsigned int element_pos;
  std::tie(element_idx, element_pos) = get_element_and_pos<T>(index);
  T *dest_eptr = dest + element_idx;
  if (set_bit) {
    // Set the target bit
    *dest_eptr |= (1 << element_pos);
  } else {
    // Clear the target bit
    *dest_eptr &= ~(1 << element_pos);
  }
}

}  // namespace softrvv
#endif  // SOFTRVV_INTERNAL_H