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    <p>Using ToString is about 10x faster than Jon Skeet's solution. While this is reasonably fast, the challenge here (if there are any takers!) is to beat the performance of ToString.</p> <p>The performance results I get from the following test program are: ShowInfo 239 ms FastInfo 25 ms</p> <pre><code>using System; using System.Diagnostics; using System.Globalization; public class Test { static public void Main(string[] x) { Stopwatch sw1 = new Stopwatch(); Stopwatch sw2 = new Stopwatch(); sw1.Start(); for (int i = 0; i &lt; 10000; i++) { ShowInfo(123.4500m); ShowInfo(0m); ShowInfo(0.0m); ShowInfo(12.45m); ShowInfo(12.4500m); ShowInfo(770m); } sw1.Stop(); sw2.Start(); for (int i = 0; i &lt; 10000; i++) { FastInfo(123.4500m); FastInfo(0m); FastInfo(0.0m); FastInfo(12.45m); FastInfo(12.4500m); FastInfo(770m); } sw2.Stop(); Console.WriteLine(sw1.ElapsedMilliseconds); Console.WriteLine(sw2.ElapsedMilliseconds); Console.ReadLine(); } // Be aware of how this method handles edge cases. // A few are counterintuitive, like the 0.0 case. // Also note that the goal is to report a precision // and scale that can be used to store the number in // an SQL DECIMAL type, so this does not correspond to // how precision and scale are defined for scientific // notation. The minimal precision SQL decimal can // be calculated by subtracting TrailingZeros as follows: // DECIMAL(Precision - TrailingZeros, Scale - TrailingZeros). // // dec Precision Scale TrailingZeros // ------- --------- ----- ------------- // 0 1 0 0 // 0.0 2 1 1 // 0.1 1 1 0 // 0.01 2 2 0 [Diff result than ShowInfo] // 0.010 3 3 1 [Diff result than ShowInfo] // 12.45 4 2 0 // 12.4500 6 4 2 // 770 3 0 0 static DecimalInfo FastInfo(decimal dec) { string s = dec.ToString(CultureInfo.InvariantCulture); int precision = 0; int scale = 0; int trailingZeros = 0; bool inFraction = false; bool nonZeroSeen = false; foreach (char c in s) { if (inFraction) { if (c == '0') trailingZeros++; else { nonZeroSeen = true; trailingZeros = 0; } precision++; scale++; } else { if (c == '.') { inFraction = true; } else if (c != '-') { if (c != '0' || nonZeroSeen) { nonZeroSeen = true; precision++; } } } } // Handles cases where all digits are zeros. if (!nonZeroSeen) precision += 1; return new DecimalInfo(precision, scale, trailingZeros); } struct DecimalInfo { public int Precision { get; private set; } public int Scale { get; private set; } public int TrailingZeros { get; private set; } public DecimalInfo(int precision, int scale, int trailingZeros) : this() { Precision = precision; Scale = scale; TrailingZeros = trailingZeros; } } static DecimalInfo ShowInfo(decimal dec) { // We want the integer parts as uint // C# doesn't permit int[] to uint[] conversion, // but .NET does. This is somewhat evil... uint[] bits = (uint[])(object)decimal.GetBits(dec); decimal mantissa = (bits[2] * 4294967296m * 4294967296m) + (bits[1] * 4294967296m) + bits[0]; uint scale = (bits[3] &gt;&gt; 16) &amp; 31; // Precision: number of times we can divide // by 10 before we get to 0 uint precision = 0; if (dec != 0m) { for (decimal tmp = mantissa; tmp &gt;= 1; tmp /= 10) { precision++; } } else { // Handle zero differently. It's odd. precision = scale + 1; } uint trailingZeros = 0; for (decimal tmp = mantissa; tmp % 10m == 0 &amp;&amp; trailingZeros &lt; scale; tmp /= 10) { trailingZeros++; } return new DecimalInfo((int)precision, (int)scale, (int)trailingZeros); } } </code></pre>
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    1. POCalculate System.Decimal Precision and Scale
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    1. USJason Kresowaty
    1. USJason Kresowaty
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    1. COI'm not entirely surprised - we're doing a lot of operations with decimals simply due to the lack of a 96-bit integer type. If you use ulong instead of decimal for the mantissa by completely ignoring the top 32 bits, it's slightly faster than FastInfo - but of course, it doesn't work for all decimals! I suspect we can improve the speed by counting both the precision and the trailing zeros in one loop (as both divide by 10 each time).
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      1. USJon Skeet
    2. COThe string-based algorithm produces incorrect results for numbers with leading zeros, i.e., 0.555, and numbers that have zeros between the decimal and significant digits, i.e., 0.0005.
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      1. USJon Seigel
    3. CO<produces incorrect results> Thanks, I have adapted the code. I have also added a comment to the code above the FastInfo method. This is to point out that the method uses SQL precision and scale definitions, not the usual scientific notation ones. (The mention that this is to deal with SQL decimals was in the original question.)
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