Mega Code Archive
Convert a string of hex digits to a byte array, with the first byte in the array being the MSB
<![CDATA[
import java.util.StringTokenizer;
/* Copyright (c) 2008 Google Inc.
*
* 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.google.gdata.util.common.base;
/**
* Some common string manipulation utilities.
*/
public class Util{
/**
* Convert a string of hex digits to a byte array, with the first
* byte in the array being the MSB. The string passed in should be
* just the raw digits (upper or lower case), with no leading
* or trailing characters (like '0x' or 'h').
* An odd number of characters is supported.
* If the string is empty, an empty array will be returned.
*
* This is significantly faster than using
* new BigInteger(str, 16).toByteArray();
* especially with larger strings. Here are the results of some
* microbenchmarks done on a P4 2.8GHz 2GB RAM running
* linux 2.4.22-gg11 and JDK 1.5 with an optimized build:
*
* String length hexToBytes (usec) BigInteger
* -----------------------------------------------------
* 16 0.570 1.43
* 256 8.21 44.4
* 1024 32.8 526
* 16384 546 121000
*/
public static byte[] hexToBytes(String str) {
byte[] bytes = new byte[(str.length() + 1) / 2];
if (str.length() == 0) {
return bytes;
}
bytes[0] = 0;
int nibbleIdx = (str.length() % 2);
for (int i = 0; i < str.length(); i++) {
char c = str.charAt(i);
if (!isHex(c)) {
throw new IllegalArgumentException("string contains non-hex chars");
}
if ((nibbleIdx % 2) == 0) {
bytes[nibbleIdx >> 1] = (byte) (hexValue(c) << 4);
} else {
bytes[nibbleIdx >> 1] += (byte) hexValue(c);
}
nibbleIdx++;
}
return bytes;
}
private static boolean isHex(char c) {
return ((c >= '0') && (c <= '9')) ||
((c >= 'a') && (c <= 'f')) ||
((c >= 'A') && (c <= 'F'));
}
private static int hexValue(char c) {
if ((c >= '0') && (c <= '9')) {
return (c - '0');
} else if ((c >= 'a') && (c <= 'f')) {
return (c - 'a') + 10;
} else {
return (c - 'A') + 10;
}
}
}
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