From 32c131bb44489c8ee32573e63da7e530f8656e1e Mon Sep 17 00:00:00 2001
From: Greg Hurrell <greg@hurrell.net>
Date: Fri, 31 Jul 2015 19:46:18 -0700
Subject: [PATCH] Implement `convert` function

Along with some illustrative tests. More to come (will fill in the blank
`it` blocks).

Based on the technique described at:

http://www.danvk.org/hex2dec.html
---
 src/__tests__/convert-test.js | 92 +++++++++++++++++++++++++++++++++++
 src/convert.js                | 37 ++++++++++++++
 2 files changed, 129 insertions(+)
 create mode 100644 src/__tests__/convert-test.js
 create mode 100644 src/convert.js

diff --git a/src/__tests__/convert-test.js b/src/__tests__/convert-test.js
new file mode 100644
index 0000000..5df1fca
--- /dev/null
+++ b/src/__tests__/convert-test.js
@@ -0,0 +1,92 @@
+/**
+ * Copyright 2015-present Greg Hurrell. All rights reserved.
+ * Licensed under the terms of the MIT license.
+ */
+
+'use strict';
+
+import convert from '../convert';
+
+describe('convert()', () => {
+  describe('converting from binary', () => {
+    it('treats binary-to-binary as a no-op', () => {
+      expect(convert('1011001', 2, 2)).toBe('1011001');
+    });
+
+    it('converts binary to decimal', () => {
+    });
+
+    it('converts binary to octal', () => {
+    });
+
+    it('converts binary to hexadecimal', () => {
+    });
+
+    it('converts with arbitrary precision', () => {
+    });
+  });
+
+  describe('converting from decimal', () => {
+    it('treats decimal-to-decimal as a no-op', () => {
+      expect(convert('324234124', 10, 10)).toBe('324234124');
+    });
+
+    it('converts decimal to binary', () => {
+    });
+
+    it('converts decimal to octal', () => {
+    });
+
+    it('converts decimal to hexadecimal', () => {
+      expect(convert('255', 10, 16)).toBe('ff');
+      expect(convert('4277009102', 10, 16)).toBe('feedface');
+    });
+
+    it('converts with arbitrary precision', () => {
+    });
+  });
+
+  describe('converting from octal', () => {
+    it('treats octal-to-octal as a no-op', () => {
+      expect(convert('723147234234', 8, 8)).toBe('723147234234');
+    });
+
+    it('converts octal to binary', () => {
+    });
+
+    it('converts octal to decimal', () => {
+    });
+
+    it('converts octal to hexadecimal', () => {
+    });
+
+    it('converts with arbitrary precision', () => {
+    });
+  });
+
+  describe('converting form hexadecimal', () => {
+    it('treats hexadecimal-to-hexadecimal as a no-op', () => {
+      expect(convert('deadbeef', 16, 16)).toBe('deadbeef');
+    });
+
+    it('converts hexadecimal to binary', () => {
+    });
+
+    it('converts hexadecimal to decimal', () => {
+      expect(convert('ff', 16, 10)).toBe('255');
+      expect(convert('feedface', 16, 10)).toBe('4277009102');
+    });
+
+    it('converts hexadecimal to octal', () => {
+    });
+
+    it('converts with arbitrary precision', () => {
+      expect(convert('ab92b650b5f18fb53ee9f6229fd82638d069d9af', 16, 10))
+        .toBe('979509212510335489186816896981475731336057182639');
+      expect(convert('ab92b650b5f18fb53ee9f6229fd82638d069d9af', 16, 8))
+        .toBe('125622554502657430766517564766105177301143432032354657');
+      expect(convert('ab92b650b5f18fb53ee9f6229fd82638d069d9af', 16, 2))
+        .toBe('1010101110010010101101100101000010110101111100011000111110110101001111101110100111110110001000101001111111011000001001100011100');
+    });
+  });
+});
diff --git a/src/convert.js b/src/convert.js
new file mode 100644
index 0000000..75e8ee3
--- /dev/null
+++ b/src/convert.js
@@ -0,0 +1,37 @@
+/**
+ * Copyright 2015-present Greg Hurrell. All rights reserved.
+ * Licensed under the terms of the MIT license.
+ *
+ * @flow
+ */
+
+'use strict';
+
+import addDigits from './addDigits';
+import getDigits from './getDigits';
+import joinDigits from './joinDigits';
+import multiplyDigits from './multiplyDigits';
+
+/**
+ * Convert `number` in base `inBase`, to base `outBase`.
+ */
+export default function convert(
+  number: string,
+  inBase: number,
+  outBase: number
+): string {
+  const digits = getDigits(number, inBase);
+  let result = [0];
+  let power = [1];
+  for (let i = 0; i < digits.length; i++) {
+    if (digits[i]) {
+      result = addDigits(
+        result,
+        multiplyDigits(power, digits[i], outBase),
+        outBase
+      );
+    }
+    power = multiplyDigits(power, inBase, outBase);
+  }
+  return joinDigits(result, outBase);
+}
-- 
2.37.1