FixedWidthInteger

NOTE: The maximum value is 4999. The minimum value is 1. Out of range values are returned as “”.

Inspired by the SO answer here: https://stackoverflow.com/a/36068105/879365

This method allows us to mask a discrete bit range within the number, and return its value as a 64-bit 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 useful for interpeting bitfields, such as the OBD DTS response.

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.

Bit 1 is the least signficant (rightmost) bit in the value. The maximum value for firstPlace is 64. Run Length means the selected (by firstPlace) first bit, and leftward (towards more significant bits). It includes the first bit.

The UInt64 variant of this is the “main” one.

• prerequisites:

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