Function SignedBitfieldPlus

src/common/bitfield_util.cc:39–79

See also https://github.com/redis/redis/blob/7f4bae817614988c43c3024402d16edcbf3b3277/src/bitops.c#L325

// See also https://github.com/redis/redis/blob/7f4bae817614988c43c3024402d16edcbf3b3277/src/bitops.c#L325
StatusOr<bool> SignedBitfieldPlus(uint64_t value, int64_t incr, uint8_t bits, BitfieldOverflowBehavior overflow,
                                  uint64_t *dst) {
  Status bits_status(BitfieldEncoding::CheckSupportedBitLengths(BitfieldEncoding::Type::kSigned, bits));
  if (!bits_status) {
    return bits_status;
  }

  auto max = std::numeric_limits<int64_t>::max();
  if (bits != 64) {
    max = (static_cast<int64_t>(1) << (bits - 1)) - 1;
  }
  int64_t min = -max - 1;

  int64_t signed_value = CastToSignedWithoutBitChanges(value);
  int64_t max_incr = CastToSignedWithoutBitChanges(static_cast<uint64_t>(max) - value);
  int64_t min_incr = min - signed_value;

  if (signed_value > max || (bits != 64 && incr > max_incr) || (signed_value >= 0 && incr >= 0 && incr > max_incr)) {
    if (overflow == BitfieldOverflowBehavior::kWrap) {
      *dst = WrappedSignedBitfieldPlus(value, incr, bits);
    } else if (overflow == BitfieldOverflowBehavior::kSat) {
      *dst = max;
    } else {
      CHECK(overflow == BitfieldOverflowBehavior::kFail);
    }
    return true;
  } else if (signed_value < min || (bits != 64 && incr < min_incr) ||
             (signed_value < 0 && incr < 0 && incr < min_incr)) {
    if (overflow == BitfieldOverflowBehavior::kWrap) {
      *dst = WrappedSignedBitfieldPlus(value, incr, bits);
    } else if (overflow == BitfieldOverflowBehavior::kSat) {
      *dst = min;
    } else {
      CHECK(overflow == BitfieldOverflowBehavior::kFail);
    }
    return true;
  }

  *dst = signed_value + incr;
  return false;
}

static uint64_t WrappedUnsignedBitfieldPlus(uint64_t value, int64_t incr, uint8_t bits) {
  uint64_t mask = std::numeric_limits<uint64_t>::max() << bits;