Friday, February 03, 2012

Fast Conversion of Hex String Into Decimal Number

Today's post will be about performance. More specifically about converting hex string into decimal number faster than using built-in .NET Framework methods.

I will compare performance of three methods used to convert hex into decimal number. Two of those methods are built into .NET Framework.

1) Convert.ToInt32(hexNumberString, 16)
2) int.Parse(hexNumber, NumberStyles.HexNumber);
3) Custom method using pre-populated table. Let us call it TableConvert.

Here's the code for the TableConvert class. This class just illustrates the idea behind pre-populated table - it is not production code.

class TableConvert
      static sbyte[] unhex_table =
      { -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1
       , 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,-1,-1,-1,-1,-1,-1
      public static int Convert(string hexNumber)
          int decValue = unhex_table[(byte)hexNumber[0]];
          for (int i = 1; i < hexNumber.Length; i++)
              decValue *= 16;
              decValue += unhex_table[(byte)hexNumber[i]];
          return decValue;

The approach uses simple technique of pre-populated table of  hex-to-decimal values and some simple math. To measure performance of these three methods I've wrote small test application that performed conversion in the loop and measured time.

Tests were made using Intel Core i7 2.80 GHz, .NET Framework 4.0. Time measurements were made in ticks using Stopwatch class.

Hex string: FF01

IterationsTableConvertConvert MethodParse Method

Hex string: 4AB201
IterationsTableConvertConvert MethodParse Method

Not surprisingly Parse method has the worst performance of all methods. While TableConvert method is the fastest. Usually about 1.2 - 1.4 times faster (20%-40%) than Convert Method.

If you ever happen to do a lot of  convert operations of hex string into decimal number and want to perform it as fast as possible - you can use TableConvert method.

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