Stop using charAt for Signatures

Simply getting the byte array and operating on that instead of using
String.charAt() repeatedly speeds up Signature initializer calls during
bootup from 150ms to 9ms (1700% faster).

Change-Id: I85ef17ef63477927e0181d5f49a1d521b7b0d98b

1 files changed, 16 insertions, 9 deletions

diff --git a/core/java/android/content/pm/Signature.java b/core/java/android/content/pm/Signature.java
index d4e5cc1..b32664e 100644
--- a/core/java/android/content/pm/Signature.java
+++ b/core/java/android/content/pm/Signature.java
@@ -45,16 +45,23 @@ public class Signature implements Parcelable {
      * {@link #toChars} or {@link #toCharsString()}.
      */
     public Signature(String text) {
-        final int N = text.length()/2;
-        byte[] sig = new byte[N];
-        for (int i=0; i<N; i++) {
-            char c = text.charAt(i*2);
-            byte b = (byte)(
-                    (c >= 'a' ? (c - 'a' + 10) : (c - '0'))<<4);
-            c = text.charAt(i*2 + 1);
-            b |= (byte)(c >= 'a' ? (c - 'a' + 10) : (c - '0'));
-            sig[i] = b;
+        final byte[] input = text.getBytes();
+        final int N = input.length;
+        final byte[] sig = new byte[N / 2];
+        int sigIndex = 0;
+
+        for (int i = 0; i < N;) {
+            int b;
+
+            final int hi = input[i++];
+            b = (hi >= 'a' ? (hi - 'a' + 10) : (hi - '0')) << 4;
+
+            final int lo = input[i++];
+            b |= (lo >= 'a' ? (lo - 'a' + 10) : (lo - '0')) & 0x0F;
+
+            sig[sigIndex++] = (byte) (b & 0xFF);
         }
+
         mSignature = sig;
     }