precision: multiple increment/decrement

Signed-off-by: Christoph Ruegg <git@cdrnet.ch>

src/Numerics/Precision.cs

@@ -243,11 +243,31 @@ namespace MathNet.Numerics
         /// <returns>The next larger floating point value.</returns>
         public static double Increment(this double value)
         {
-            if (double.IsInfinity(value) || double.IsNaN(value))
+            return Increment(value, 1);
+        }
+
+        /// <summary>
+        /// Increments a floating point number to the next bigger number representable by the data type.
+        /// </summary>
+        /// <param name="value">The value which needs to be incremented.</param>
+        /// <param name="count">How many times the number should be incremented.</param>
+        /// <remarks>
+        /// The incrementation step length depends on the provided value.
+        /// Increment(double.MaxValue) will return positive infinity.
+        /// </remarks>
+        /// <returns>The next larger floating point value.</returns>
+        public static double Increment(this double value, int count)
+        {
+            if (double.IsInfinity(value) || double.IsNaN(value) || count == 0)
             {
                 return value;
             }
 
+            if (count < 0)
+            {
+                Decrement(value, -count);
+            }
+
             // Translate the bit pattern of the double to an integer.
             // Note that this leads to:
             // double > 0 --> long > 0, growing as the double value grows
@@ -257,11 +277,11 @@ namespace MathNet.Numerics
             long intValue = GetLongFromDouble(value);
             if (intValue < 0)
             {
-                intValue--;
+                intValue -= count;
             }
             else
             {
-                intValue++;
+                intValue += count;
             }
 
             // Note that long.MinValue has the same bit pattern as -0.0.
@@ -286,11 +306,31 @@ namespace MathNet.Numerics
         /// <returns>The next smaller floating point value.</returns>
         public static double Decrement(this double value)
         {
-            if (double.IsInfinity(value) || double.IsNaN(value))
+            return Decrement(value, 1);
+        }
+
+        /// <summary>
+        /// Decrements a floating point number to the next smaller number representable by the data type.
+        /// </summary>
+        /// <param name="value">The value which should be decremented.</param>
+        /// <param name="count">How many times the number should be decremented.</param>
+        /// <remarks>
+        /// The decrementation step length depends on the provided value.
+        /// Decrement(double.MinValue) will return negative infinity.
+        /// </remarks>
+        /// <returns>The next smaller floating point value.</returns>
+        public static double Decrement(this double value, int count)
+        {
+            if (double.IsInfinity(value) || double.IsNaN(value) || count == 0)
             {
                 return value;
             }
 
+            if (count < 0)
+            {
+                Decrement(value, -count);
+            }
+
             // Translate the bit pattern of the double to an integer.
             // Note that this leads to:
             // double > 0 --> long > 0, growing as the double value grows
@@ -309,11 +349,11 @@ namespace MathNet.Numerics
 
             if (intValue < 0)
             {
-                intValue++;
+                intValue += count;
             }
             else
             {
-                intValue--;
+                intValue -= count;
             }
 
             // Note that not all long values can be translated into double values. There's a whole bunch of them