From aff7fda17d14951584cfe5622f2ee3996afd4162 Mon Sep 17 00:00:00 2001
From: Mike Hearn <hearn@google.com>
Date: Wed, 20 Apr 2011 15:47:41 +0000
Subject: [PATCH] Add a function/some tests for string to nanocoin conversions
 and vice-versa, along with a TODO to clean this whole thing up. Patch from
 Thilo Planz.

Fixes issue 1.
---
 src/com/google/bitcoin/core/Utils.java       | 32 +++++++++++++-
 tests/com/google/bitcoin/core/UtilsTest.java | 46 ++++++++++++++++++++
 2 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 tests/com/google/bitcoin/core/UtilsTest.java

diff --git a/src/com/google/bitcoin/core/Utils.java b/src/com/google/bitcoin/core/Utils.java
index 9e0785fd..fb90aaa6 100644
--- a/src/com/google/bitcoin/core/Utils.java
+++ b/src/com/google/bitcoin/core/Utils.java
@@ -20,6 +20,7 @@ import com.google.bitcoin.bouncycastle.crypto.digests.RIPEMD160Digest;
 
 import java.io.IOException;
 import java.io.OutputStream;
+import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
@@ -30,9 +31,24 @@ import java.security.NoSuchAlgorithmException;
  */
 @SuppressWarnings({"SameParameterValue"})
 public class Utils {
-    /** How many nanocoins there are in a BitCoin. */
+    // TODO: Replace this nanocoins business with something better.
+
+    /**
+     * How many "nanocoins" there are in a BitCoin.
+     *
+     * A nanocoin is the smallest unit that can be transferred using BitCoin.
+     * The term nanocoin is very misleading, though, because there are only 100 million
+     * of them in a coin (whereas one would expect 1 billion.
+     */
     public static final BigInteger COIN = new BigInteger("100000000", 10);
-    /** How many nanocoins there are in 0.01 BitCoins. */
+
+    /**
+     * How many "nanocoins" there are in 0.01 BitCoins.
+     *
+     * A nanocoin is the smallest unit that can be transferred using BitCoin.
+     * The term nanocoin is very misleading, though, because there are only 100 million
+     * of them in a coin (whereas one would expect 1 billion).
+     */
     public static final BigInteger CENT = new BigInteger("1000000", 10);
 
     private static final boolean logging;
@@ -49,6 +65,18 @@ public class Utils {
         return bi;
     }
 
+    /**
+     * Convert an amount expressed in the way humans are used to into nanocoins.<p>
+     *
+     * This takes string in a format understood by {@link BigDecimal#BigDecimal(String)},
+     * for example "0", "1", "0.10", "1.23E3", "1234.5E-5".
+     * 
+     * @throws ArithmeticException if you try to specify fractional nanocoins
+     **/
+    public static BigInteger toNanoCoins(String coins){
+        return new BigDecimal(coins).movePointRight(8).toBigIntegerExact();
+    }
+
     public static void uint32ToByteArrayBE(long val, byte[] out, int offset) {
         out[offset + 0] = (byte) (0xFF & (val >> 24));
         out[offset + 1] = (byte) (0xFF & (val >> 16));
diff --git a/tests/com/google/bitcoin/core/UtilsTest.java b/tests/com/google/bitcoin/core/UtilsTest.java
new file mode 100644
index 00000000..7bf312a8
--- /dev/null
+++ b/tests/com/google/bitcoin/core/UtilsTest.java
@@ -0,0 +1,46 @@
+/**
+ * Copyright 2011 Thilo Planz
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.bitcoin.core;
+
+import static junit.framework.Assert.assertEquals;
+import static junit.framework.Assert.fail;
+
+import org.junit.Test;
+
+public class UtilsTest {
+
+    @Test
+    public void testToNanoCoins() {
+        // String version
+        assertEquals(Utils.CENT, Utils.toNanoCoins("0.01"));
+        assertEquals(Utils.CENT, Utils.toNanoCoins("1E-2"));
+        assertEquals(Utils.COIN.add(Utils.CENT), Utils.toNanoCoins("1.01"));
+        try {
+            Utils.toNanoCoins("2E-20");
+            fail("should not have accepted fractional nanocoins");
+        } catch (ArithmeticException e) {
+        }
+
+        // int version
+        assertEquals(Utils.CENT, Utils.toNanoCoins(0, 1));
+
+        // TODO: should this really pass?
+        assertEquals(Utils.COIN.subtract(Utils.CENT), Utils.toNanoCoins(1, -1));
+        assertEquals(Utils.COIN.negate(), Utils.toNanoCoins(-1, 0));
+        assertEquals(Utils.COIN.negate(), Utils.toNanoCoins("-1"));
+    }
+}