Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.11)
// Compass (v1.0.3)
// ----


@function math-pow($number, $exp) {
    @if (round($exp) != $exp) {
      @return math-exp($exp * math-ln($number));
    }
    
    // Traditional method for integers
    $value: 1;
    
    @if $exp > 0 {
        @for $i from 1 through $exp {
           $value: $value * $number;
        }
    }
    @else if $exp < 0 {
        @for $i from 1 through -$exp {
            $value: $value / $number;
        }
    }

    @return $value;
}

@function math-factorial($value) {
  @if $value == 0 {
    @return 1;
  }
  
  $result: 1;
  
  @for $index from 1 through $value {
    $result: $result * $index;
  }
  
  @return $result;
}

@function math-summation($iteratee, $input, $initial: 0, $limit: 100) {
  $sum: 0;
  
  @for $index from $initial to $limit {
    $sum: $sum + call($iteratee, $input, $index);
  }
  
  @return $sum;
}

@function math-exp-maclaurin($x, $n) {
  $result: math-pow($x, $n) / math-factorial($n);
  @return $result;
}
@function math-exp($value) {
  $result: math-summation(math-exp-maclaurin, $value, 0, 100);
  @return $result;
}

@function math-ln-maclaurin($x, $n) {
  $result: (math-pow(-1, $n + 1) / $n) * (math-pow($x - 1, $n));
  @return $result;
}
@function math-ln($value) {
  $ten-exp: 1;
  $ln-ten: 2.30258509;
  
  @while ($value > math-pow(10, $ten-exp)) {
    $ten-exp: $ten-exp + 1;
  }
  
  $value: $value / math-pow(10, $ten-exp);

  $result: math-summation(math-ln-maclaurin, $value, 1, 100);
  
  @return $result + $ten-exp * $ln-ten;
}

.test {
  input: 'math-pow(3, 2)';
  expected: 9;
  actual: math-pow(3, 2);
  input: 'math-pow(4, 3/2)';
  expected: 8;
  actual: math-pow(4, 3/2);
  input: 'math-pow(144, 1/2)';
  expected: 12;
  actual: math-pow(144, 1/2);
  input: 'math-pow(-3, 2)';
  expected: 9;
  actual: math-pow(-3, 2);
  input: 'math-pow(3, -2)';
  expected: 0.1111;
  actual: math-pow(3, -2);
  input: 'math-pow(64, -1/2)';
  expected: 0.125;
  actual: math-pow(64, -1/2);
  input: 'math-pow(12, 3.4)';
  expected: 4668.91789313;
  actual: math-pow(12, 3.4);
}

SassMeister-output.css

.test {
  input: 'math-pow(3, 2)';
  expected: 9;
  actual: 9;
  input: 'math-pow(4, 3/2)';
  expected: 8;
  actual: 8.0;
  input: 'math-pow(144, 1/2)';
  expected: 12;
  actual: 12.0;
  input: 'math-pow(-3, 2)';
  expected: 9;
  actual: 9;
  input: 'math-pow(3, -2)';
  expected: 0.1111;
  actual: 0.11111;
  input: 'math-pow(64, -1/2)';
  expected: 0.125;
  actual: 0.125;
  input: 'math-pow(12, 3.4)';
  expected: 4668.91789313;
  actual: 4668.92127;
}

The idea of using taylor/maclaurin expansions is great, but the implementation is very inefficient. For example the implementation of math-pow uses linear time, while it could be implemented in logarithmic time. Also for the series themselves you could save the factorial and power of each step instead of calculating it all again for the next one.

I tried to do a more efficient implementation at http://www.sassmeister.com/gist/5bbe8480c48e2fc10ab5. It compiles about 100 times faster while producing more output (I added sin). What do you think of it?

Thank you both :-)
@xi hope you don't mind me linking to your sass-planifolia repo :-)