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;
}

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