C# extension methods for the Decimal class.

``````using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ExtensionOverflow
{
/// <summary>
/// Decimal Extensions
/// </summary>
public static class DecimalExtensions
{
#region PercentageOf calculations

/// <summary>
/// The numbers percentage
/// </summary>
/// <param name="number">The number.</param>
/// <param name="percent">The percent.</param>
/// <returns>The result</returns>
public static decimal PercentageOf(this decimal number, int percent)
{
return (decimal)(number * percent / 100);
}

/// <summary>
/// Percentage of the number.
/// </summary>
/// <param name="percent">The percent</param>
/// <param name="number">The Number</param>
/// <returns>The result</returns>
public static decimal PercentOf(this decimal position, int total)
{
decimal result = 0;
if (position > 0 && total > 0)
{
result = (decimal)position / (decimal)total * 100;
}
return result;
}

/// <summary>
/// The numbers percentage
/// </summary>
/// <param name="number">The number.</param>
/// <param name="percent">The percent.</param>
/// <returns>The result</returns>
public static decimal PercentageOf(this decimal number, decimal percent)
{
return (decimal)(number * percent / 100);
}

/// <summary>
/// Percentage of the number.
/// </summary>
/// <param name="percent">The percent</param>
/// <param name="number">The Number</param>
/// <returns>The result</returns>
public static decimal PercentOf(this decimal position, decimal total)
{
decimal result = 0;
if (position > 0 && total > 0)
{
result = (decimal)position / (decimal)total * 100;
}
return result;
}

/// <summary>
/// The numbers percentage
/// </summary>
/// <param name="number">The number.</param>
/// <param name="percent">The percent.</param>
/// <returns>The result</returns>
public static decimal PercentageOf(this decimal number, long percent)
{
return (decimal)(number * percent / 100);
}

/// <summary>
/// Percentage of the number.
/// </summary>
/// <param name="percent">The percent</param>
/// <param name="number">The Number</param>
/// <returns>The result</returns>
public static decimal PercentOf(this decimal position, long total)
{
decimal result = 0;
if (position > 0 && total > 0)
{
result = (decimal)position / (decimal)total * 100;
}
return result;
}

#endregion

/// <summary>
/// Extension method to round a double value to a fixed number of significant figures instead of a fixed decimal places.
/// </summary>
/// <param name="d">Double we're rounding</param>
/// <param name="digits">Number of significant figures</param>
/// <returns>New double rounded to digits-significant figures</returns>
public static decimal RoundToSignificantDigits(this decimal d, int digits)
{
if (d == 0) return 0;
var scale = (decimal)Math.Pow(10, Math.Floor(Math.Log10((double) Math.Abs(d))) + 1);
return scale * Math.Round(d / scale, digits);
}

/// <summary>
/// Provides global smart rounding, numbers larger than 1000 will round to 4 decimal places,
/// while numbers smaller will round to 7 significant digits
/// </summary>
public static decimal SmartRounding(this decimal input)
{
input = Normalize(input);

// any larger numbers we still want some decimal places
if (input > 1000)
{
return Math.Round(input, 4);
}

// this is good for forex and other small numbers
var d = (double)input;
return (decimal)d.RoundToSignificantDigits(7);
}

public static decimal Normalize(this decimal input)
{
// http://stackoverflow.com/a/7983330/1582922
return input / 1.000000000000000000000000000000000m;
}

public static decimal Normalize(this decimal input)
{
// http://stackoverflow.com/a/7983330/1582922
return input / 1.000000000000000000000000000000000m;
}

/// <summary>
/// Extension method for faster string to decimal conversion.
/// </summary>
/// <param name="str">String to be converted to positive decimal value</param>
/// <remarks>
/// Method makes some assuptions - always numbers, no "signs" +,- etc.
/// Leading and trailing whitespace chars are ignored
/// </remarks>
/// <returns>Decimal value of the string</returns>
public static decimal ToDecimal(this string str)
{
long value = 0;
var decimalPlaces = 0;
var hasDecimals = false;
var index = 0;
var length = str.Length;

while (index < length && char.IsWhiteSpace(str[index]))
{
index++;
}

while (index < length)
{
var ch = str[index++];
if (ch == '.')
{
hasDecimals = true;
decimalPlaces = 0;
}
else if (char.IsWhiteSpace(ch))
{
break;
}
else
{
value = value * 10 + (ch - '0');
decimalPlaces++;
}
}

var lo = (int)value;
var mid = (int)(value >> 32);
return new decimal(lo, mid, 0, false, (byte)(hasDecimals ? decimalPlaces : 0));
}

}
}``````