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Faster byte and word to hex string

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I was alarmed to discover just how slow `String.format()` is for doing
integer to hex conversions. Now that a trace window has been added to
Symon, it became especially clear that I needed a more efficient way to
handle it.

I looked into using `Integer.toHexString()`, but I would have had to
wrap it to do zero-padding, so I decided to just bite the bullet and do
my own with a lookup table. The implementation in `HexUtil` is just as
fast as `Integer.toHexString()`, but also zero-pads appropriately.
Combined with Java's `+` String concatenation, it seems perfectly
adequate.

For yet better performance with the trace window, it would make a lot of
sense to special-case stepping so that it just pops the top line off the
log, and appends to the bottom, rather than re-stringifying the entire
trace log each time. This will be a future enhancement.
This commit is contained in:
Seth Morabito committed 2012-12-09 21:02:11 -08:00
1 parent bc3de80892
commit 807a43ce6f
5 files changed
+225 -56
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src/main/java/com/loomcom/symon/util/HexUtil.java
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package com.loomcom.symon.util;
/**
* Hex String Utilities.
*
* <p/>
*
* But why? Java, after all, has a number of ways to convert an integer into a hex string,
* so it may look absurd to go to the trouble of writing yet another conversion! The answer is
* performance.
*
* <p/>
*
* The most convenient way to get a formatted hex value from an integer is with the <code>String.format</code>
* method, but this turns out to be extremely inefficient. Formatting a million integers
* with <code>String.format</code> takes something like 1600ms. Formatting the same number of integers
* with <code>HexUtil</code> takes only 160ms. This is on part with <code>Integer.toHexString</code>,
* but also allows the desired padding.
*
*/
public class HexUtil {
private static final String[] HEX_CONSTANTS = {"00", "01", "02", "03", "04", "05", "06", "07",
"08", "09", "0A", "0B", "0C", "0D", "0E", "0F",
"10", "11", "12", "13", "14", "15", "16", "17",
"18", "19", "1A", "1B", "1C", "1D", "1E", "1F",
"20", "21", "22", "23", "24", "25", "26", "27",
"28", "29", "2A", "2B", "2C", "2D", "2E", "2F",
"30", "31", "32", "33", "34", "35", "36", "37",
"38", "39", "3A", "3B", "3C", "3D", "3E", "3F",
"40", "41", "42", "43", "44", "45", "46", "47",
"48", "49", "4A", "4B", "4C", "4D", "4E", "4F",
"50", "51", "52", "53", "54", "55", "56", "57",
"58", "59", "5A", "5B", "5C", "5D", "5E", "5F",
"60", "61", "62", "63", "64", "65", "66", "67",
"68", "69", "6A", "6B", "6C", "6D", "6E", "6F",
"70", "71", "72", "73", "74", "75", "76", "77",
"78", "79", "7A", "7B", "7C", "7D", "7E", "7F",
"80", "81", "82", "83", "84", "85", "86", "87",
"88", "89", "8A", "8B", "8C", "8D", "8E", "8F",
"90", "91", "92", "93", "94", "95", "96", "97",
"98", "99", "9A", "9B", "9C", "9D", "9E", "9F",
"A0", "A1", "A2", "A3", "A4", "A5", "A6", "A7",
"A8", "A9", "AA", "AB", "AC", "AD", "AE", "AF",
"B0", "B1", "B2", "B3", "B4", "B5", "B6", "B7",
"B8", "B9", "BA", "BB", "BC", "BD", "BE", "BF",
"C0", "C1", "C2", "C3", "C4", "C5", "C6", "C7",
"C8", "C9", "CA", "CB", "CC", "CD", "CE", "CF",
"D0", "D1", "D2", "D3", "D4", "D5", "D6", "D7",
"D8", "D9", "DA", "DB", "DC", "DD", "DE", "DF",
"E0", "E1", "E2", "E3", "E4", "E5", "E6", "E7",
"E8", "E9", "EA", "EB", "EC", "ED", "EE", "EF",
"F0", "F1", "F2", "F3", "F4", "F5", "F6", "F7",
"F8", "F9", "FA", "FB", "FC", "FD", "FE", "FF"};
/**
* Very fast 8-bit int to hex conversion, with zero-padded output.
*
* @param val The unsigned 8-bit value to convert to a zero padded hexadecimal string.
* @return Two digit, zero padded hexadecimal string.
*/
public static String byteToHex(int val) {
return HEX_CONSTANTS[val & 0xff];
}
/**
* Very fast 16-bit int to hex conversion, with zero-padded output.
*
* @param val The unsigned 16-bit value to convert to a zero padded hexadecimal string.
* @return Four digit, zero padded hexadecimal string.
*/
public static String wordToHex(int val) {
StringBuilder sb = new StringBuilder(4);
sb.append(HEX_CONSTANTS[(val >> 8) & 0xff]);
sb.append(HEX_CONSTANTS[val & 0xff]);
return sb.toString();
}
}