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POPerformance question: Fastest way to convert hexadecimal char to its number value in Java?
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copied!<p>I want to convert from char representing a hexadecimal value (in upper or lower case) to byte, like</p> <pre><code>'0'->0, '1' -> 1, 'A' -> 10, 'a' -> 10, 'f' -> 15 etc... </code></pre> <p>I will be calling this method extremely often, so performance is important. Is there a faster way than to use a pre-initialized <code>HashMap<Character,Byte></code> to get the value from?</p> <p><strong>Answer</strong></p> <p>It seems like <s>it's a tossup between using a switch-case and Jon Skeet's direct computing solution - the switch-case solution seems to edge out ever so slightly, though.</s> Greg's array method wins out. Here are the performance results (in ms) for 200,000,000 runs of the various methods:</p> <pre><code>Character.getNumericValue: 8360 Character.digit: 8453 HashMap<Character,Byte>: 15109 Greg's Array Method: 6656 JonSkeet's Direct Method: 7344 Switch: 7281 </code></pre> <p>Thanks guys!</p> <p><strong>Benchmark method code</strong></p> <p>Here ya go, JonSkeet, you old competitor. ;-)</p> <pre><code>public class ScratchPad { private static final int NUMBER_OF_RUNS = 200000000; static byte res; static HashMap<Character, Byte> map = new HashMap<Character, Byte>() {{ put( Character.valueOf( '0' ), Byte.valueOf( (byte )0 )); put( Character.valueOf( '1' ), Byte.valueOf( (byte )1 )); put( Character.valueOf( '2' ), Byte.valueOf( (byte )2 )); put( Character.valueOf( '3' ), Byte.valueOf( (byte )3 )); put( Character.valueOf( '4' ), Byte.valueOf( (byte )4 )); put( Character.valueOf( '5' ), Byte.valueOf( (byte )5 )); put( Character.valueOf( '6' ), Byte.valueOf( (byte )6 )); put( Character.valueOf( '7' ), Byte.valueOf( (byte )7 )); put( Character.valueOf( '8' ), Byte.valueOf( (byte )8 )); put( Character.valueOf( '9' ), Byte.valueOf( (byte )9 )); put( Character.valueOf( 'a' ), Byte.valueOf( (byte )10 )); put( Character.valueOf( 'b' ), Byte.valueOf( (byte )11 )); put( Character.valueOf( 'c' ), Byte.valueOf( (byte )12 )); put( Character.valueOf( 'd' ), Byte.valueOf( (byte )13 )); put( Character.valueOf( 'e' ), Byte.valueOf( (byte )14 )); put( Character.valueOf( 'f' ), Byte.valueOf( (byte )15 )); put( Character.valueOf( 'A' ), Byte.valueOf( (byte )10 )); put( Character.valueOf( 'B' ), Byte.valueOf( (byte )11 )); put( Character.valueOf( 'C' ), Byte.valueOf( (byte )12 )); put( Character.valueOf( 'D' ), Byte.valueOf( (byte )13 )); put( Character.valueOf( 'E' ), Byte.valueOf( (byte )14 )); put( Character.valueOf( 'F' ), Byte.valueOf( (byte )15 )); }}; static int[] charValues = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13,14,15,-1,-1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,10, 11, 12, 13,14,15}; static char[] cs = new char[]{'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f','A','B','C','D','E','F'}; public static void main(String args[]) throws Exception { long time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { res = getNumericValue( i ); } System.out.println( "Character.getNumericValue:" ); System.out.println( System.currentTimeMillis()-time ); time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { res = getDigit( i ); } System.out.println( "Character.digit:" ); System.out.println( System.currentTimeMillis()-time ); time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { try { res = getValueFromArray( i ); } catch (IllegalArgumentException e) { } } System.out.println( "Array:" ); System.out.println( System.currentTimeMillis()-time ); time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { res = getValueFromHashMap( i ); } System.out.println( "HashMap<Character,Byte>:" ); System.out.println( System.currentTimeMillis()-time ); time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { char c = cs[i%cs.length]; res = getValueFromComputeMethod( c ); } System.out.println( "JonSkeet's Direct Method:" ); System.out.println( System.currentTimeMillis()-time ); time = System.currentTimeMillis(); for( int i = 0; i < NUMBER_OF_RUNS; i++ ) { res = getValueFromSwitch( i ); } System.out.println( "Switch:" ); System.out.println( System.currentTimeMillis()-time ); } private static byte getValueFromSwitch( int i ) { byte res; char ch = cs[i%cs.length]; switch( ch ) { case '0': res = 0; break; case '1': res = 1; break; case '2': res = 2; break; case '3': res = 3; break; case '4': res = 4; break; case '5': res = 5; break; case '6': res = 6; break; case '7': res = 7; break; case '8': res = 8; break; case '9': res = 9; break; case 'a': case 'A': res = 10; break; case 'b': case 'B': res = 11; break; case 'c': case 'C': res = 12; break; case 'd': case 'D': res = 13; break; case 'e': case 'E': res = 14; break; case 'f': case 'F': res = 15; break; default: throw new RuntimeException("unknown hex character: " + ch ); } return res; } private static byte getValueFromComputeMethod( char c ) { byte result = 0; if (c >= '0' && c <= '9') { result = (byte)(c - '0'); } if (c >= 'a' && c <= 'f') { result = (byte)(c - 'a' + 10); } if (c >= 'A' && c <= 'F') { result = (byte)(c - 'A' + 10); } return result; } private static byte getValueFromHashMap( int i ) { return map.get( Character.valueOf( cs[i%cs.length] ) ).byteValue(); } private static byte getValueFromArray( int i ) { char c = cs[i%cs.length]; if (c < '0' || c > 'f') { throw new IllegalArgumentException(); } byte result = (byte)charValues[c-'0']; if (res < 0) { throw new IllegalArgumentException(); } return result; } private static byte getDigit( int i ) { return (byte)Character.digit( cs[i%cs.length], 16 ); } private static byte getNumericValue( int i ) { return (byte)Character.getNumericValue( cs[i%cs.length] ); } } </code></pre>

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