Struggling to find the source code for truncatingIfNeeded

carlos42421 · 2020-07-03T11:31:22.650Z

I know this shouldn't be so difficult, but I can't find where the initialiser for integer types init(truncatingIfNeeded:) ... is located in the standard library source code!

Can anyone point it out? Is there something more mysterious going on or I just can't see the wood for the trees!

cukr · 2020-07-03T11:43:54.330Z

This?

github.com

apple/swift/blob/2938466ecb6554da1bf01b52b78c7dbce82ff0af/stdlib/public/core/Integers.swift#L3157


      
          ///     let x = Int16(truncatingIfNeeded: w)
          ///     // x == -21
          ///     // 'x' has a binary representation of 11111111_11101011
          ///     let y = UInt16(truncatingIfNeeded: w)
          ///     // y == 65515
          ///     // 'y' has a binary representation of 11111111_11101011
          ///
          /// - Parameter source: An integer to convert to this type.
          @inlinable // FIXME(inline-always)
          @inline(__always)
          public init<T: BinaryInteger>(truncatingIfNeeded source: T) {
            if Self.bitWidth <= Int.bitWidth {
              self = Self(_truncatingBits: source._lowWord)
            }
            else {
              let neg = source < (0 as T)
              var result: Self = neg ? ~0 : 0
              var shift: Self = 0
              let width = Self(_truncatingBits: Self.bitWidth._lowWord)
              for word in source.words {
                guard shift < width else { break }

carlos42421 · 2020-07-03T11:48:12.021Z

Yes!!

Thank goodness. I was going mad...

I think I need to take a break. Thank you.