Check arches in order of preference

The documentation for Build.SUPPORTED_ABIS says:
"An ordered list of ABIs supported by this device. The most preferred
ABI is the first element in the list."

Respect that preference when checking for which arch to install
packages for.

Fixes #131.

app/build.gradle

@@ -13,8 +13,8 @@ android {
         applicationId "com.termux"
         minSdkVersion 21
         targetSdkVersion 24
-        versionCode 38
-        versionName "0.38"
+        versionCode 39
+        versionName "0.39"
 
         ndk {
             moduleName "libtermux"

app/src/main/java/com/termux/app/ExtraKeysView.java

@@ -165,8 +165,8 @@ public final class ExtraKeysView extends GridLayout {
                 param.rightMargin = param.topMargin = 0;
                 param.setGravity(Gravity.LEFT);
                 float weight = "▲▼◀▶".contains(buttonText) ? 0.7f : 1.f;
-                param.columnSpec = GridLayout.spec(col, weight);
-                param.rowSpec = GridLayout.spec(row, 1.f);
+                param.columnSpec = GridLayout.spec(col, GridLayout.FILL, weight);
+                param.rowSpec = GridLayout.spec(row, GridLayout.FILL, 1.f);
                 button.setLayoutParams(param);
 
                 addView(button);

app/src/main/java/com/termux/app/TermuxInstaller.java

@@ -26,7 +26,9 @@ import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipInputStream;
 
@@ -184,25 +186,28 @@ final class TermuxInstaller {
 
     /** Get bootstrap zip url for this systems cpu architecture. */
     static URL determineZipUrl() throws MalformedURLException {
-        String termuxArch = null;
+        String archName = determineTermuxArchName();
+        return new URL("https://termux.net/bootstrap/bootstrap-" + archName + ".zip");
+    }
+
+    private static String determineTermuxArchName() {
         // Note that we cannot use System.getProperty("os.arch") since that may give e.g. "aarch64"
         // while a 64-bit runtime may not be installed (like on the Samsung Galaxy S5 Neo).
         // Instead we search through the supported abi:s on the device, see:
         // http://developer.android.com/ndk/guides/abis.html
-        // Note that we search for abi:s in preferred order, and want to avoid installing arm on
-        // an x86 system where arm emulation is available.
-        final String[] androidArchNames = {"arm64-v8a", "x86_64", "x86", "armeabi-v7a"};
-        final String[] termuxArchNames = {"aarch64", "x86_64", "i686", "arm"};
-
-        final List<String> supportedArches = Arrays.asList(Build.SUPPORTED_ABIS);
-        for (int i = 0; i < termuxArchNames.length; i++) {
-            if (supportedArches.contains(androidArchNames[i])) {
-                termuxArch = termuxArchNames[i];
-                break;
+        // Note that we search for abi:s in preferred order (the ordering of the
+        // Build.SUPPORTED_ABIS list) to avoid e.g. installing arm on an x86 system where arm
+        // emulation is available.
+        for (String androidArch : Build.SUPPORTED_ABIS) {
+            switch (androidArch) {
+                case "arm64-v8a": return "aarch64";
+                case "armeabi-v7a": return "arm";
+                case "x86_64": return "x86_64";
+                case "x86": return "i686";
             }
         }
-
-        return new URL("https://termux.net/bootstrap/bootstrap-" + termuxArch + ".zip");
+        throw new RuntimeException("Unable to determine arch from Build.SUPPORTED_ABIS =  " +
+            Arrays.toString(Build.SUPPORTED_ABIS));
     }
 
     /** Delete a folder and all its content or throw. */