Replacing FloatMath native implementation with calls to Math

On modern versions of Android running in AOT mode
FloatMath is slower than Math. Calls to Math.sqrt(),
etc. are replaced by intrinsics which can be as small
as a single CPU opcode.

When running in interpreted mode the new
implementation is unfortunately slower, but I'm
judging this acceptable and likely to be improved
over time. This change saves a small amount of native
code.

Example timings:

Mako AOSP AOT:

Method: Original / New / Direct call to Math
ceil: 596ns / 146.ns / 111ns
sqrt: 694ns / 56ns / 25ns

Mako AOSP interpreted:

Method: Original / New / Direct call to Math
ceil: 1900ns / 2307ns / 1485ns
sqrt: 1998ns / 2603ns / 1788ns

Other calls Mako AOT:

Method: Original / New
cos: 635ns / 270ns
exp: 566ns / 324ns
floor: 604ns / 150ns
hypot: 631ns / 232ns
pow: 936ns / 643ns
sin: 641ns / 299ns

The advice to use Math directly, in preference to
FloatMath, is still good. FloatMath will be deprecated
separately.

Bug: https://code.google.com/p/android/issues/detail?id=36199
Change-Id: I8d1947d88b3c576643138b1df589fb9da7c1ab88

core/java/android/util/FloatMath.java

@@ -17,10 +17,13 @@
 package android.util;
 
 /**
- * Math routines similar to those found in {@link java.lang.Math}. On
- * versions of Android with a JIT, these are significantly slower than
- * the equivalent {@code Math} functions, which should be used in preference
- * to these.
+ * 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.
  */
 public class FloatMath {
 

core/jni/Android.mk

@@ -80,7 +80,6 @@ LOCAL_SRC_FILES:= \
 	android_util_Binder.cpp \
 	android_util_EventLog.cpp \
 	android_util_Log.cpp \
-	android_util_FloatMath.cpp \
 	android_util_Process.cpp \
 	android_util_StringBlock.cpp \
 	android_util_XmlBlock.cpp \

core/jni/AndroidRuntime.cpp

@@ -90,8 +90,6 @@ extern int register_android_media_AudioTrack(JNIEnv *env);
 extern int register_android_media_JetPlayer(JNIEnv *env);
 extern int register_android_media_ToneGenerator(JNIEnv *env);
 
-extern int register_android_util_FloatMath(JNIEnv* env);
-
 namespace android {
 
 /*
@@ -1229,7 +1227,6 @@ static const RegJNIRec gRegJNI[] = {
     REG_JNI(register_android_os_SystemClock),
     REG_JNI(register_android_util_EventLog),
     REG_JNI(register_android_util_Log),
-    REG_JNI(register_android_util_FloatMath),
     REG_JNI(register_android_content_AssetManager),
     REG_JNI(register_android_content_StringBlock),
     REG_JNI(register_android_content_XmlBlock),

core/jni/android_util_FloatMath.cpp

@@ -1,61 +0,0 @@
-#include "jni.h"
-#include <android_runtime/AndroidRuntime.h>
-#include <math.h>
-#include <float.h>
-#include "SkTypes.h"
-
-class MathUtilsGlue {
-public:
-    static float FloorF(JNIEnv* env, jobject clazz, float x) {
-        return floorf(x);
-    }
-    
-    static float CeilF(JNIEnv* env, jobject clazz, float x) {
-        return ceilf(x);
-    }
-    
-    static float SinF(JNIEnv* env, jobject clazz, float x) {
-        return sinf(x);
-    }
-    
-    static float CosF(JNIEnv* env, jobject clazz, float x) {
-        return cosf(x);
-    }
-    
-    static float SqrtF(JNIEnv* env, jobject clazz, float x) {
-        return sqrtf(x);
-    }
-
-    static float ExpF(JNIEnv* env, jobject clazz, float x) {
-        return expf(x);
-    }
-
-    static float PowF(JNIEnv* env, jobject clazz, float x, float y) {
-        return powf(x, y);
-    }
-
-    static float HypotF(JNIEnv* env, jobject clazz, float x, float y) {
-        return hypotf(x, y);
-    }
-};
-
-static JNINativeMethod gMathUtilsMethods[] = {
-    {"floor", "(F)F", (void*) MathUtilsGlue::FloorF},
-    {"ceil", "(F)F", (void*) MathUtilsGlue::CeilF},
-    {"sin", "(F)F", (void*) MathUtilsGlue::SinF},
-    {"cos", "(F)F", (void*) MathUtilsGlue::CosF},
-    {"sqrt", "(F)F", (void*) MathUtilsGlue::SqrtF},
-    {"exp", "(F)F", (void*) MathUtilsGlue::ExpF},
-    {"pow", "(FF)F", (void*) MathUtilsGlue::PowF},
-    {"hypot", "(FF)F", (void*) MathUtilsGlue::HypotF},
-};
-
-int register_android_util_FloatMath(JNIEnv* env)
-{
-    int result = android::AndroidRuntime::registerNativeMethods(env,
-                                            "android/util/FloatMath",
-                                            gMathUtilsMethods,
-                                            SK_ARRAY_COUNT(gMathUtilsMethods));
-    return result;
-}
-

core/tests/benchmarks/src/android/util/FloatMathBenchmark.java

@@ -0,0 +1,103 @@
+package android.util;
+
+import com.google.caliper.Param;
+import com.google.caliper.Runner;
+import com.google.caliper.SimpleBenchmark;
+
+import android.util.FloatMath;
+
+import dalvik.system.VMDebug;
+
+public class FloatMathBenchmark extends SimpleBenchmark {
+
+    public float timeFloatMathCeil(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.ceil(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathCeil_math(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += (float) Math.ceil(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathCos(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.cos(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathExp(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.exp(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathFloor(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.floor(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathHypot(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.hypot(100.123f, 100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathPow(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.pow(10.123f, 10.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathSin(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.sin(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathSqrt(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += FloatMath.sqrt(100.123f);
+        }
+        return f;
+    }
+
+    public float timeFloatMathSqrt_math(int reps) {
+        // Keep an answer so we don't optimize the method call away.
+        float f = 0.0f;
+        for (int i = 0; i < reps; i++) {
+            f += (float) Math.sqrt(100.123f);
+        }
+        return f;
+    }
+
+}