Convert Double-String to Int64 after multiplying by 100 gives wrong value

Using Swift
,
2

  1. Are you sure you shouldn't be using Decimal? It sounds like you're maybe doing what Decimal is for.

  2. Int64's initializer doesn't round. It truncates.

Swift has unit tests that look like this:

@Test func test() {
  #expect(convertAmount("0.29") == 29)
  #expect(convertAmount("0.58") == 58)
  #expect(convertAmount("16.08") == 16_08)
  #expect(convertAmount("1025.12") == 1025_12)
}

If you're using Int64, I don't know that NSDecimalNumber is available to you. If it is…

func convertAmount(_ amount: String?) -> Int64 {
  guard let decimal = amount.flatMap({ Decimal(string: $0) })
  else { return 0 }

  return .init(truncating: decimal * 100 as NSDecimalNumber)
}

If not,

func convertAmount(_ amount: String?) -> Int64 {
  guard let double = amount.flatMap(Double.init)
  else { return 0 }

  return .init((double  * 100).rounded())
}
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