Decimal init performance #123
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tgymnich
reviewed
Nov 7, 2024
| guard integer.sign == .plus else { return nil } | ||
| assert(integer.floatingPointClass == .positiveNormal) | ||
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| let significand = BigUInt("\(integer.significand)")! |
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There seems to be a public-ish field called _mantissa in Decimal which should be faster than using the string representation here. Maybe we should use this and keep the above arround maybe commented out just in case _mantissa goes away one day.
public var _mantissa: (UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt16)
tgymnich
approved these changes
Nov 7, 2024
tgymnich
reviewed
Nov 7, 2024
| @@ -53,6 +53,7 @@ extension BigUInt { | |||
| let byteCount = (self.bitWidth + 7) / 8 | |||
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| let buffer = UnsafeMutableBufferPointer<UInt8>.allocate(capacity: byteCount) | |||
| buffer.initialize(repeating: 0) | |||
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Works, but setting the remaining bytes (0..<i) to zero after the loop below could be more efficient.
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Awesome thank you. Left a few ideas for future improvements. |
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Well I figured out how signifcands and exponents work.... Or at least well enough to make the initializer much faster now.
I added a test to use the largest and smallest Decimal values as extreme cases and, while I don't know how long it took with the old method, it was longer than walking away and coming back to the computer. Now it's a fraction of a second.
I also made a quick safety fix to a buffer method since I caught it right after my last contribution.