lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/MathDetector.java

/*
 * Copyright (C) 2011 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 com.android.tools.lint.checks;

import com.android.annotations.NonNull;
import com.android.annotations.Nullable;
import com.android.tools.lint.detector.api.Category;
import com.android.tools.lint.detector.api.Detector;
import com.android.tools.lint.detector.api.Implementation;
import com.android.tools.lint.detector.api.Issue;
import com.android.tools.lint.detector.api.JavaContext;
import com.android.tools.lint.detector.api.Location;
import com.android.tools.lint.detector.api.Scope;
import com.android.tools.lint.detector.api.Severity;
import com.android.tools.lint.detector.api.SourceCodeScanner;
import com.intellij.psi.PsiMethod;
import java.util.Arrays;
import java.util.List;
import org.jetbrains.uast.UCallExpression;

/**
 * Looks for usages of {@link Math} methods which can be replaced with {@code
 * android.util.FloatMath} methods to avoid casting.
 */
public class MathDetector extends Detector implements SourceCodeScanner {
    /** The main issue discovered by this detector */
    public static final Issue ISSUE =
            Issue.create(
                            "FloatMath",
                            "Using `FloatMath` instead of `Math`",
                            "In older versions of Android, using `android.util.FloatMath` was recommended "
                                    + "for performance reasons when operating on floats. However, on modern hardware "
                                    + "doubles are just as fast as float (though they take more memory), and in "
                                    + "recent versions of Android, `FloatMath` is actually slower than using `java.lang.Math` "
                                    + "due to the way the JIT optimizes `java.lang.Math`. Therefore, you should use "
                                    + "`Math` instead of `FloatMath` if you are only targeting Froyo and above.",
                            Category.PERFORMANCE,
                            3,
                            Severity.WARNING,
                            new Implementation(MathDetector.class, Scope.JAVA_FILE_SCOPE))
                    .addMoreInfo(
                            "http://developer.android.com/guide/practices/design/performance.html#avoidfloat")
                    .setAndroidSpecific(true);

    /** Constructs a new {@link MathDetector} check */
    public MathDetector() {}

    // ---- implements SourceCodeScanner ----

    @Nullable
    @Override
    public List<String> getApplicableMethodNames() {
        return Arrays.asList("sin", "cos", "ceil", "sqrt", "floor");
    }

    @Override
    public void visitMethodCall(
            @NonNull JavaContext context,
            @NonNull UCallExpression call,
            @NonNull PsiMethod method) {
        if (context.getEvaluator().isMemberInClass(method, "android.util.FloatMath")
                && context.getProject().getMinSdk() >= 8) {
            String message =
                    String.format(
                            "Use `java.lang.Math#%1$s` instead of `android.util.FloatMath#%1$s()` "
                                    + "since it is faster as of API 8",
                            method.getName());
            Location location = context.getCallLocation(call, true, false);
            context.report(ISSUE, call, location, message);
        }
    }
}