src/support/bits.h

/*
 * Copyright 2015 WebAssembly Community Group participants
 *
 * 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 wasm_support_bits_h
#define wasm_support_bits_h

#include <array>
#include <climits>
#include <cstdint>
#include <cstring>
#include <type_traits>

/*
 * Portable bit functions.
 *
 * Not all platforms offer fast intrinsics for these functions, and some
 * compilers require checking CPUID at runtime before using the intrinsic.
 *
 * We instead use portable and reasonably-fast implementations, while
 * avoiding implementations with large lookup tables.
 */

namespace wasm::Bits {

int popCount(uint8_t);
int popCount(uint16_t);
int popCount(uint32_t);
int popCount(uint64_t);

inline int popCount(int8_t v) { return popCount(uint8_t(v)); }
inline int popCount(int16_t v) { return popCount(uint16_t(v)); }
inline int popCount(int32_t v) { return popCount(uint32_t(v)); }
inline int popCount(int64_t v) { return popCount(uint64_t(v)); }

uint32_t bitReverse(uint32_t);

int countTrailingZeroes(uint32_t);
int countTrailingZeroes(uint64_t);

inline int countTrailingZeroes(int32_t v) {
  return countTrailingZeroes(uint32_t(v));
}
inline int countTrailingZeroes(int64_t v) {
  return countTrailingZeroes(uint64_t(v));
}

int countLeadingZeroes(uint32_t);
int countLeadingZeroes(uint64_t);

inline int countLeadingZeroes(int32_t v) {
  return countLeadingZeroes(uint32_t(v));
}
inline int countLeadingZeroes(int64_t v) {
  return countLeadingZeroes(uint64_t(v));
}

int ceilLog2(uint32_t);
int ceilLog2(uint64_t);

inline int ceilLog2(int32_t v) { return ceilLog2(uint32_t(v)); }
inline int ceilLog2(int64_t v) { return ceilLog2(uint64_t(v)); }

template<typename T> bool isPowerOf2(T v) {
  return v != 0 && (v & (v - 1)) == 0;
}

bool isPowerOf2InvertibleFloat(float);
bool isPowerOf2InvertibleFloat(double);

template<typename T, typename U> inline static T rotateLeft(T val, U count) {
  auto value = typename std::make_unsigned<T>::type(val);
  U mask = sizeof(T) * CHAR_BIT - 1;
  count &= mask;
  return (value << count) | (value >> (-count & mask));
}
template<typename T, typename U> inline static T rotateRight(T val, U count) {
  auto value = typename std::make_unsigned<T>::type(val);
  U mask = sizeof(T) * CHAR_BIT - 1;
  count &= mask;
  return (value >> count) | (value << (-count & mask));
}

uint32_t log2(uint32_t v);
uint32_t pow2(uint32_t v);

template<
  typename T,
  typename std::enable_if<
    std::is_same<T, typename std::array<uint8_t, std::tuple_size<T>::value>>::
      value,
    bool>::type = true>
void writeLE(T val, void* ptr) {
  memcpy(ptr, val.data(), sizeof(T));
}

template<typename T,
         typename std::enable_if<std::is_integral<T>::value, bool>::type = true>
void writeLE(T val, void* ptr) {
  auto v = typename std::conditional<std::is_signed<T>::value,
                                     typename std::make_unsigned<T>::type,
                                     T>::type(val);
  unsigned char* buf = reinterpret_cast<unsigned char*>(ptr);
#pragma GCC unroll 10
  for (size_t i = 0; i < sizeof(T); ++i) {
    buf[i] = v >> (CHAR_BIT * i);
  }
}

template<
  typename T,
  typename std::enable_if<
    std::is_same<T, typename std::array<uint8_t, std::tuple_size<T>::value>>::
      value,
    bool>::type = true>
T readLE(const void* ptr) {
  T v;
  memcpy(v.data(), ptr, sizeof(T));
  return v;
}

template<typename T,
         typename std::enable_if<std::is_integral<T>::value, bool>::type = true>
T readLE(const void* ptr) {
  using TU = typename std::conditional<std::is_signed<T>::value,
                                       typename std::make_unsigned<T>::type,
                                       T>::type;
  TU v = 0;
  const unsigned char* buf = reinterpret_cast<const unsigned char*>(ptr);
#pragma GCC unroll 10
  for (size_t i = 0; i < sizeof(T); ++i) {
    v += (TU)buf[i] << (CHAR_BIT * i);
  }
  return v;
}

} // namespace wasm::Bits

#endif // wasm_support_bits_h