Add exponential math functions. (#909)

CHANGELOG.md

@@ -5,6 +5,11 @@
     in between `$min` and `$max`.
   * `hypot()`: given *n* numbers, outputs the length of the *n*-dimensional
     vector that has components equal to each of the inputs.
+  * Exponential (all inputs must be unitless):
+    * `log($number)` or `log($number, $base)`. If no base is provided, `log()`
+      performs a natural log.
+    * `pow($base, $exponent)`
+    * `sqrt($number)`
 
 * Add the variables `$pi` and `$e` to the built-in "sass:math" module.
 

lib/src/functions/math.dart

@@ -23,8 +23,8 @@ final global = UnmodifiableListView([
 
 /// The Sass math module.
 final module = BuiltInModule("math", functions: [
-  _abs, _ceil, _clamp, _compatible, _floor, _hypot, _isUnitless, _max, _min, //
-  _percentage, _randomFunction, _round, _unit,
+  _abs, _ceil, _clamp, _compatible, _floor, _hypot, _isUnitless, _log, _max, //
+  _min, _pow, _percentage, _randomFunction, _round, _sqrt, _unit,
 ], variables: {
   "e": SassNumber(math.e),
   "pi": SassNumber(math.pi),
@@ -133,6 +133,86 @@ final _hypot = BuiltInCallable("hypot", r"$numbers...", (arguments) {
       numeratorUnits: numeratorUnits, denominatorUnits: denominatorUnits);
 });
 
+///
+/// Exponential functions
+///
+
+final _log = BuiltInCallable("log", r"$number, $base: null", (arguments) {
+  var number = arguments[0].assertNumber("number");
+  if (number.hasUnits) {
+    throw SassScriptException("\$number: Expected $number to have no units.");
+  }
+
+  var numberValue = fuzzyEquals(number.value, 0) ? 0 : number.value;
+
+  if (arguments[1] == sassNull) return SassNumber(math.log(numberValue));
+
+  var base = arguments[1].assertNumber("base");
+  if (base.hasUnits) {
+    throw SassScriptException("\$base: Expected $base to have no units.");
+  }
+
+  var baseValue = fuzzyEquals(base.value, 0) || fuzzyEquals(base.value, 1)
+      ? fuzzyRound(base.value)
+      : base.value;
+
+  return SassNumber(math.log(numberValue) / math.log(baseValue));
+});
+
+final _pow = BuiltInCallable("pow", r"$base, $exponent", (arguments) {
+  var base = arguments[0].assertNumber("base");
+  var exponent = arguments[1].assertNumber("exponent");
+
+  if (base.hasUnits) {
+    throw SassScriptException("\$base: Expected $base to have no units.");
+  } else if (exponent.hasUnits) {
+    throw SassScriptException(
+        "\$exponent: Expected $exponent to have no units.");
+  }
+
+  var baseValue = base.value;
+  var exponentValue = exponent.value;
+
+  if (fuzzyEquals(baseValue.abs(), 1) && exponentValue.isInfinite) {
+    return SassNumber(double.nan);
+  }
+
+  // Exponentiating certain real numbers leads to special behaviors. Ensure that
+  // these behaviors are consistent for numbers within the precision limit.
+  if (fuzzyEquals(exponentValue, 0)) {
+    exponentValue = 0;
+  } else if (fuzzyEquals(baseValue, 0)) {
+    baseValue = baseValue.isNegative ? -0.0 : 0;
+    if (exponentValue.isFinite &&
+        fuzzyIsInt(exponentValue) &&
+        fuzzyAsInt(exponentValue) % 2 == 1) {
+      exponentValue = fuzzyRound(exponentValue);
+    }
+  } else if (baseValue.isFinite &&
+      fuzzyLessThan(baseValue, 0) &&
+      exponentValue.isFinite &&
+      fuzzyIsInt(exponentValue)) {
+    exponentValue = fuzzyRound(exponentValue);
+  } else if (baseValue.isInfinite &&
+      fuzzyLessThan(baseValue, 0) &&
+      exponentValue.isFinite &&
+      fuzzyIsInt(exponentValue) &&
+      fuzzyAsInt(exponentValue) % 2 == 1) {
+    exponentValue = fuzzyRound(exponentValue);
+  }
+
+  return SassNumber(math.pow(baseValue, exponentValue));
+});
+
+final _sqrt = BuiltInCallable("sqrt", r"$number", (arguments) {
+  var number = arguments[0].assertNumber("number");
+  if (number.hasUnits) {
+    throw SassScriptException("\$number: Expected $number to have no units.");
+  }
+
+  return SassNumber(math.sqrt(number.value));
+});
+
 ///
 /// Unit functions
 ///