Bugforces (ft. senile logarithmic exponentiation)

Sad things happen when you lose your mind:

using i64 = long long;

// Precondition: (base, exponent) won't cause overflow
i64
my_pow(const i64 base, const i64 exponent)
{
  i64 accumulator = 0;
  for (i64 exponent2 = exponent, current_power = base; exponent2 > 0;
      exponent2 >>= 1, current_pow *= current_pow)
  {
    if (exponent2 & 1)
    {
      accumulator += current_power;
    }
  }
  return accumulator;
}

Bugforces (ft Education Codeforces Round 86)

Consider the following implementation to find the smallest multiple of x at least as big as y:

typedef long long i64;

i64
next_mult_ge(const i64 y, const i64 x)
{
    return ceil(y / (double) x) * x;
}

What can go wrong?