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November 19, 2015 [Issue 15365] std.math: 80-bit exp() tests are utterly wrong when returning subnormals | ||||
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 | https://issues.dlang.org/show_bug.cgi?id=15365 Iain Buclaw <ibuclaw@gdcproject.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ibuclaw@gdcproject.org Severity|enhancement |major -- | |||
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ReplyNovember 20, 2015 [Issue 15365] std.math: 80-bit exp() tests are utterly wrong when returning subnormals | ||||
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 | https://issues.dlang.org/show_bug.cgi?id=15365 --- Comment #1 from Don <clugdbug@yahoo.com.au> --- Note that these errors occur only in the slow path of the asm exp(). Thus, a more accurate, slower calculation can be added with no impact on speed. Clearly, there is a loss of precision bug. I am not certain, but the problem may be in the extraction of the integer part, which is obviously limited to 64 bits. I need to look into this. This title of this bug report is a bit alarmist though, it's not very generous to describe 52 bit accurate as "utterly wrong". :) -- | |||
November 20, 2015 [Issue 15365] std.math: 80-bit exp() tests are utterly wrong when returning subnormals | ||||
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| https://issues.dlang.org/show_bug.cgi?id=15365 --- Comment #2 from Iain Buclaw <ibuclaw@gdcproject.org> --- (In reply to Don from comment #1) > Note that these errors occur only in the slow path of the asm exp(). Thus, a more accurate, slower calculation can be added with no impact on speed. > > Clearly, there is a loss of precision bug. I am not certain, but the problem > may be in the extraction of the integer part, which is obviously limited to > 64 bits. > I need to look into this. > > This title of this bug report is a bit alarmist though, it's not very generous to describe 52 bit accurate as "utterly wrong". :) What about 5 bit accuracy? :-P -- | |||
November 22, 2015 [Issue 15365] std.math: 80-bit exp() tests are utterly wrong when returning subnormals | ||||
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| https://issues.dlang.org/show_bug.cgi?id=15365 --- Comment #3 from Iain Buclaw <ibuclaw@gdcproject.org> --- Stepped through the path dmd code uses for exp(). (1) 0x1.1p13L - Uses L_normal path (2) -0x1.18p+13L - Uses L_normal path (3) -0x1.625p+13L - Uses L_normal path (4) -0x1.62dafp+13L - Uses L_normal path Interestingly, the last test exp(-11398) uses the L_subnormal path, and returns results that are correct to wolfram in at least the bits that can be represented. Also tried exp(-11370) and exp(-11387.4), and on the surface it looks like any near underflow/subnormal that represents a decimal will only be correct up to double precision. Also tested the first iteration of exp() and it returns the same results. -- | |||
December 12, 2017 [Issue 15365] std.math: 80-bit exp() tests are marginally wrong when returning subnormals | ||||
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| https://issues.dlang.org/show_bug.cgi?id=15365 Iain Buclaw <ibuclaw@gdcproject.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|std.math: 80-bit exp() |std.math: 80-bit exp() |tests are utterly wrong |tests are marginally wrong |when returning subnormals |when returning subnormals -- | |||
December 17, 2022 [Issue 15365] std.math: 80-bit exp() tests are marginally wrong when returning subnormals | ||||
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| https://issues.dlang.org/show_bug.cgi?id=15365 Iain Buclaw <ibuclaw@gdcproject.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Priority|P1 |P2 -- | |||
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