UInt

This method allows us to mask a discrete bit range within the number, and return its value as a basic unsigned Int.

For example, if we have the hex number 0xF30 (3888 decimal, or 111100110000 binary), we can mask parts of it to get masked values, like so:

   // 111100110000 (Value, in binary)

   // 111111111111 (Mask, in binary)
   let wholeValue = 3888.maskedValue(firstPlace: 0, runLength: 12)     // Returns 3888
   // 111111110000
   let lastByte = 3888.maskedValue(firstPlace: 4, runLength: 8)        // Returns 243
   // 000000000011
   let lowestTwoBits = 3888.maskedValue(firstPlace: 0, runLength: 2)   // Returns 0
   // 000000111100
   let middleTwelve = 3888.maskedValue(firstPlace: 2, runLength: 4)    // Returns 12
   // 000111100000
   let middleNine = 3888.maskedValue(firstPlace: 5, runLength: 4)      // Returns 9
   // 011111111111
   let theFirstElevenBits = 3888.maskedValue(firstPlace: 0, runLength: 11) // Returns 1840
   // 111111111110
   let theLastElevenBits = 3888.maskedValue(firstPlace: 1, runLength: 11)  // Returns 1944
   // 000000110000
   let lowestTwoBitsOfTheSecondHalfOfTheFirstByte = 3888.maskedValue(firstPlace: 4, runLength: 2)          // Returns 3
   // 000001100000
   let secondToLowestTwoBitsOfTheSecondHalfOfTheFirstByte = 3888.maskedValue(firstPlace: 5, runLength: 2)  // Returns 1
   // 000011000000
   let thirdFromLowestTwoBitsOfTheSecondHalfOfTheFirstByte = 3888.maskedValue(firstPlace: 6, runLength: 2) // Returns 0

This is BIT-based, not BYTE-based, and assumes the number is in a linear (bigendian) format, in which the least significant bit is the rightmost one (position one). In reality, this doesn’t matter, as the language takes care of transposing byte order.

• prerequisites:

  • The sum of firstPlace and runLength cannot exceed the maximum size of a UInt64.