added root.js

cube_root.js

@@ -0,0 +1,10 @@
+"use strict";
+
+const root = require("./root.js");
+
+function cube_root(radicand, options) {
+  return root(radicand, "3", options);
+}
+
+module.exports = cube_root;
+module.exports.default = cube_root;

root.js

@@ -0,0 +1,73 @@
+"use strict";
+
+const absolute = require("./absolute.js");
+const clean = require("./clean.js");
+const compare_positive = require("./compare_positive.js");
+const is_even = require("./is_even.js");
+const is_negative = require("./is_negative.js");
+const pow = require("./pow.js");
+const root_integer_digits = require("./root_integer_digits.js");
+
+function root(radicand, index, { imaginary = true, max_decimal_digits = 100 } = {}) {
+  radicand = clean(radicand);
+  index = clean(index);
+
+  if (index === "1") return radicand;
+  if (radicand === "1") return "1";
+
+  const rad = absolute(radicand);
+
+  const has_imaginary = is_negative(radicand) && is_even(index);
+  if (has_imaginary && !imaginary) throw new Error("[preciso] root has an imaginary number");
+
+  const count_of_integer_places = root_integer_digits(rad, index);
+
+  const digits = ["9", "8", "7", "6", "5", "4", "3", "2", "1", "0"];
+
+  let left = "";
+
+  for (let i = 0; i < count_of_integer_places; i++) {
+    for (let ii = 0; ii < digits.length; ii++) {
+      const digit = digits[ii];
+      const test_start = left + digit;
+      let test_base = test_start + "0".repeat(count_of_integer_places - i - 1);
+      const test_res = pow(test_base, index);
+      const comparison = compare_positive(test_res, rad);
+      if (comparison === "=") {
+        if (has_imaginary) test_base += "i";
+        return test_base;
+      } else if (comparison === "<") {
+        left = test_start;
+        break;
+      }
+    }
+  }
+
+  let base = left + ".";
+
+  for (let i = 0; i < max_decimal_digits; i++) {
+    let added = false;
+    for (let ii = 0; ii < digits.length; ii++) {
+      const digit = digits[ii];
+      let test_base = base + digit;
+      const test_res = pow(test_base, index);
+      const comparison = compare_positive(test_res, rad);
+      if (comparison === "=") {
+        if (has_imaginary) test_base += "i";
+        return test_base;
+      } else if (comparison === "<") {
+        base = test_base;
+        added = true;
+        break;
+      }
+    }
+    if (!added) break;
+  }
+
+  if (has_imaginary) base += "i";
+
+  return base;
+}
+
+module.exports = root;
+module.exports.default = root;

root_integer_digits.js

@@ -0,0 +1,14 @@
+"use strict";
+
+const ceil = require("./ceil.js");
+const count_integer_digits = require("./count_integer_digits");
+const divide = require("./divide.js");
+
+function root_integer_digits(radicand, index) {
+  const digits = count_integer_digits(radicand);
+  if (digits === "0") return "0";
+  return ceil(divide(digits, index, { max_decimal_digits: 1 }));
+}
+
+module.exports = root_integer_digits;
+module.exports.default = root_integer_digits;

square_root.js

@@ -0,0 +1,10 @@
+"use strict";
+
+const root = require("./root.js");
+
+function square_root(radicand, options) {
+  return root(radicand, "2", options);
+}
+
+module.exports = square_root;
+module.exports.default = square_root;