Improve the precision of percentDownloaded in Downloaders

We don't require high precision in the calculation of `percentDownloaded` for `Downloader.ProgressListener.onProgress` though, when `byteCached == contentLength`, we hope the `percentDownloaded` to be `100f` (rather than `99.99999f`). The result of `byteCached * 100f` can be less precise as the floating-point numbers are sparser when the value is far from zero. For example, if `byteCached == 812345L`, then the `byteCached * 100f` will become `81234496` (value checked by `BigDecimal`).

PiperOrigin-RevId: 741895445

libraries/common/src/main/java/androidx/media3/common/util/Util.java

@@ -1223,6 +1223,22 @@ public final class Util {
     return result;
   }
 
+  /**
+   * Returns the percentage of numerator divided by denominator. Note that this may return {@link
+   * Float#POSITIVE_INFINITY}, {@link Float#NEGATIVE_INFINITY} or {@link Float#NaN} if the
+   * denominator is zero.
+   *
+   * @param numerator The numerator.
+   * @param denominator The denominator.
+   */
+  @UnstableApi
+  public static float percent(long numerator, long denominator) {
+    if (denominator != 0 && numerator == denominator) {
+      return 100f;
+    }
+    return ((float) numerator / denominator) * 100;
+  }
+
   /**
    * Returns the index of the first occurrence of {@code value} in {@code array}, or {@link
    * C#INDEX_UNSET} if {@code value} is not contained in {@code array}.

libraries/common/src/test/java/androidx/media3/common/util/UtilTest.java

@@ -27,6 +27,7 @@ import static androidx.media3.common.util.Util.maxValue;
 import static androidx.media3.common.util.Util.minValue;
 import static androidx.media3.common.util.Util.parseXsDateTime;
 import static androidx.media3.common.util.Util.parseXsDuration;
+import static androidx.media3.common.util.Util.percent;
 import static androidx.media3.common.util.Util.unescapeFileName;
 import static androidx.media3.test.utils.TestUtil.buildTestData;
 import static androidx.media3.test.utils.TestUtil.buildTestString;
@@ -147,6 +148,34 @@ public class UtilTest {
     assertThat(res).isEqualTo(12345);
   }
 
+  @Test
+  public void percent_numeratorEqualToDenominator_returnsOneHundred() {
+    // With numerator and denominator both being 812345L, the percentage calculated in another way
+    // (numerator * 100f / denominator) will be 99.99999f. We then use this value to verify that
+    // this doesn't happen for Util.percent() method.
+    assertThat(percent(812345L, 812345L)).isEqualTo(100f);
+  }
+
+  @Test
+  public void percent_numeratorNotEqualToDenominator_returnsCorrectValue() {
+    assertThat(percent(500L, 2000L)).isEqualTo(25f);
+  }
+
+  @Test
+  public void percent_positiveNumeratorAndZeroDenominator_returnsPositiveInfinity() {
+    assertThat(percent(1L, 0L)).isPositiveInfinity();
+  }
+
+  @Test
+  public void percent_negativeNumeratorAndZeroDenominator_returnsNegativeInfinity() {
+    assertThat(percent(-1L, 0L)).isNegativeInfinity();
+  }
+
+  @Test
+  public void percent_numeratorAndDenominatorAreBothZero_returnsNaN() {
+    assertThat(percent(0L, 0L)).isNaN();
+  }
+
   @Test
   public void inferContentType_handlesHlsIsmUris() {
     assertThat(Util.inferContentType(Uri.parse("http://a.b/c.ism/manifest(format=m3u8-aapl)")))

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/offline/ProgressiveDownloader.java

@@ -17,6 +17,7 @@ package androidx.media3.exoplayer.offline;
 
 import static androidx.annotation.VisibleForTesting.PRIVATE;
 import static androidx.media3.common.util.Assertions.checkNotNull;
+import static androidx.media3.common.util.Util.percent;
 
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
@@ -216,7 +217,7 @@ public final class ProgressiveDownloader implements Downloader {
     float percentDownloaded =
         contentLength == C.LENGTH_UNSET || contentLength == 0
             ? C.PERCENTAGE_UNSET
-            : ((bytesCached * 100f) / contentLength);
-    progressListener.onProgress(contentLength, bytesCached, percentDownloaded);
+            : percent(bytesCached, contentLength);
+    checkNotNull(progressListener).onProgress(contentLength, bytesCached, percentDownloaded);
   }
 }

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/offline/SegmentDownloader.java

@@ -16,6 +16,7 @@
 package androidx.media3.exoplayer.offline;
 
 import static androidx.media3.common.util.Assertions.checkNotNull;
+import static androidx.media3.common.util.Util.percent;
 
 import android.net.Uri;
 import androidx.annotation.Nullable;
@@ -536,9 +537,9 @@ public abstract class SegmentDownloader<M extends FilterableManifest<M>> impleme
 
     private float getPercentDownloaded() {
       if (contentLength != C.LENGTH_UNSET && contentLength != 0) {
-        return (bytesDownloaded * 100f) / contentLength;
+        return percent(bytesDownloaded, contentLength);
       } else if (totalSegments != 0) {
-        return (segmentsDownloaded * 100f) / totalSegments;
+        return percent(segmentsDownloaded, totalSegments);
       } else {
         return C.PERCENTAGE_UNSET;
       }