diff --git a/build.sbt b/build.sbt
index a0eeb512..390cb944 100644
--- a/build.sbt
+++ b/build.sbt
@@ -2,7 +2,7 @@ import android.Keys._
 
 android.Plugin.androidBuild
 
-platformTarget in Android := "android-22"
+platformTarget in Android := "android-23"
 
 name := "shadowsocks"
 
diff --git a/project/plugins.sbt b/project/plugins.sbt
index d71a8428..1a3d6e1c 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -1,6 +1,6 @@
 resolvers += Resolver.url("scalasbt releases", new URL("http://scalasbt.artifactoryonline.com/scalasbt/sbt-plugin-snapshots"))(Resolver.ivyStylePatterns)
 
-addSbtPlugin("com.hanhuy.sbt" % "android-sdk-plugin" % "1.5.0")
+addSbtPlugin("com.hanhuy.sbt" % "android-sdk-plugin" % "1.5.1")
 
 resolvers += "Sonatype snapshots" at "https://oss.sonatype.org/content/repositories/snapshots/"
 
diff --git a/src/main/AndroidManifest.xml b/src/main/AndroidManifest.xml
index 30704809..622da321 100644
--- a/src/main/AndroidManifest.xml
+++ b/src/main/AndroidManifest.xml
@@ -14,7 +14,7 @@
 
   <uses-sdk
       android:minSdkVersion="16"
-      android:targetSdkVersion="22"/>
+      android:targetSdkVersion="23"/>
 
   <application
       android:allowBackup="true"
diff --git a/src/main/java/android/util/FloatMath.java b/src/main/java/android/util/FloatMath.java
new file mode 100644
index 00000000..8f488af6
--- /dev/null
+++ b/src/main/java/android/util/FloatMath.java
@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2007 The Android Open Source Project
+ *
+ * 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 android.util;
+
+/**
+ * Math routines similar to those found in {@link java.lang.Math}.
+ *
+ * <p>Historically these methods were faster than the equivalent double-based
+ * {@link java.lang.Math} methods. On versions of Android with a JIT they
+ * became slower and have since been re-implemented to wrap calls to
+ * {@link java.lang.Math}. {@link java.lang.Math} should be used in
+ * preference.
+ *
+ * @deprecated Use {@link java.lang.Math} instead.
+ */
+@Deprecated
+public class FloatMath {
+
+    /** Prevents instantiation. */
+    private FloatMath() {}
+
+    /**
+     * Returns the float conversion of the most positive (i.e. closest to
+     * positive infinity) integer value which is less than the argument.
+     *
+     * @param value to be converted
+     * @return the floor of value
+     */
+    public static float floor(float value) {
+        return (float) Math.floor(value);
+    }
+
+    /**
+     * Returns the float conversion of the most negative (i.e. closest to
+     * negative infinity) integer value which is greater than the argument.
+     *
+     * @param value to be converted
+     * @return the ceiling of value
+     */
+    public static float ceil(float value) {
+        return (float) Math.ceil(value);
+    }
+
+    /**
+     * Returns the closest float approximation of the sine of the argument.
+     *
+     * @param angle to compute the cosine of, in radians
+     * @return the sine of angle
+     */
+    public static float sin(float angle) {
+        return (float) Math.sin(angle);
+    }
+
+    /**
+     * Returns the closest float approximation of the cosine of the argument.
+     *
+     * @param angle to compute the cosine of, in radians
+     * @return the cosine of angle
+     */
+    public static float cos(float angle) {
+        return (float) Math.cos(angle);
+    }
+
+    /**
+     * Returns the closest float approximation of the square root of the
+     * argument.
+     *
+     * @param value to compute sqrt of
+     * @return the square root of value
+     */
+    public static float sqrt(float value) {
+        return (float) Math.sqrt(value);
+    }
+
+    /**
+     * Returns the closest float approximation of the raising "e" to the power
+     * of the argument.
+     *
+     * @param value to compute the exponential of
+     * @return the exponential of value
+     */
+    public static float exp(float value) {
+        return (float) Math.exp(value);
+    }
+
+    /**
+     * Returns the closest float approximation of the result of raising {@code
+     * x} to the power of {@code y}.
+     *
+     * @param x the base of the operation.
+     * @param y the exponent of the operation.
+     * @return {@code x} to the power of {@code y}.
+     */
+    public static float pow(float x, float y) {
+        return (float) Math.pow(x, y);
+    }
+
+    /**
+     * Returns {@code sqrt(}<i>{@code x}</i><sup>{@code 2}</sup>{@code +} <i>
+     * {@code y}</i><sup>{@code 2}</sup>{@code )}.
+     *
+     * @param x a float number
+     * @param y a float number
+     * @return the hypotenuse
+     */
+    public static float hypot(float x, float y) {
+        return (float) Math.hypot(x, y);
+    }
+}