LWG-2597 std::log misspecified for complex numbers #884
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Partially address microsoft#67. Use `_Abs` and `_Copysign` instead of branching on `x < 0`, correctly treating negative zero as a negative number. This matters when branch cuts of a complex function lies on the real or the imaginary axis, where the results for positive zero and negative zero are different. The following cases are not fixed in this commit: * `pow` when the first argument is (negative - 0i). * (+/-∞ - 0i) and (-0 +/- ∞i).
|
|
AlexGuteniev
reviewed
Jun 9, 2020
For negative real number x, pow(x - 0i, y) and pow(x + 0i, y) are different: pow(x - 0i, y) = exp(y * log(x - 0i)) = exp(y * (log(|x|) - πi)) pow(x + 0i, y) = exp(y * log(x + 0i)) = exp(y * (log(|x|) + πi)) Thus pow(complex, real) couldn't simply return _Pow(real, real) when the imaginary part of the base is negative zero. This commit fixes this issue. This commit also modifies pow(complex, complex) to be consistent with pow(real, complex) when the base is a positive real number.
AlexGuteniev
reviewed
Jun 9, 2020
StephanTLavavej
approved these changes
Jun 26, 2020
statementreply
commented
Jun 26, 2020
check_norm(finite, NaN) now fires an assertion as expected.
CaseyCarter
approved these changes
Jun 26, 2020
StephanTLavavej
approved these changes
Jun 26, 2020
StephanTLavavej
approved these changes
Jun 26, 2020
CaseyCarter
approved these changes
Jun 26, 2020
CaseyCarter
changed the title
* Defend against definition of `signbit` as a function-like macro * Defend against improper promotions to `double` when computing `log(std::complex<float>)` in `/clr` mode.
CaseyCarter
reviewed
Jun 27, 2020
Annotate workaround
StephanTLavavej
approved these changes
Jun 27, 2020
|
Thank you for your contribution! I really can't overstate how much we appreciate help from domain experts. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
sqrt,asin,asinh,acos,acosh,atanandatanhof (finite - 0i) and (-0 + finite i).pow(negative - 0i, y).proj(+/-∞ - 0i)sqrtof infinities.Fix #67.
Use
_Absand_Copysigninstead of branching onx < 0, correctly treating negative zero as a negative number. This matters when branch cuts of a complex function lies on the real or the imaginary axis, where the results for positive zero and negative zero are different.