secp256k1: Return normalized val from DecompressY. #3441
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The result of the DecompressY function, as the documentation describes, currently returns a value that either has a maximum magnitude of 1 or 2 which also implies that it is not necessarily normalized either. This means the caller is currently responsible for normalization. While there is no logic issue with that approach, it does mean that callers realistically have to unconditionally normalize the result for almost all realistic use cases even though it might not actually need it. Those extra normalizations can result in a minor average comparative performance loss when amortized across millions of point decompressions. Further, putting the responsibility on the caller makes it easier make a mistake. To improve both of those cases, this updates the DecompressY function to normalize the result in all cases when the result is a valid point on the secp256k1 curve (aka the function returns true) before returning it and updates the callers accordingly. This change also means the result will now always have a max magnitude of 1.
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jrick
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Sep 19, 2024
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The result of the
DecompressYfunction, as the documentation describes, currently returns a value that either has a maximum magnitude of 1 or 2 which also implies that it is not necessarily normalized either. This means the caller is currently responsible for normalization.While there is no logic issue with that approach, it does mean that callers realistically have to unconditionally normalize the result for almost all realistic use cases even though it might not actually need it.
Those extra normalizations can result in a minor average comparative performance loss when amortized across millions of point decompressions. Further, putting the responsibility on the caller makes it easier make a mistake.
To improve both of those cases, this updates the
DecompressYfunction to normalize the result in all cases when the result is a valid point on the secp256k1 curve (aka the function returns true) before returning it and updates the callers accordingly.This change also means the result will now always have a max magnitude of 1.