I now see more clearly what the complaint is.
That said, you should ALWAYS be prepared for the round trip between binary and
string forms of floating point to accrue rounding error because floating point
is intrinsically approximate. While there are examples of floating point
numbers that can reliably do that round trip exactly (e.g. integers shorter
than the mantissa), in general you should be prepared for such "inexact"
results.
John Nash's point that IEEE754 has been relaxed is reinforcement that they want
users to be prepared for differences around the least significant bits... but
the principle is mathematically intrinsic to the scope of floating point
numbers whether the standard says so or not.
On March 9, 2025 11:06:17 AM PDT, Stephanie Evert <stefa...@collocations.de>
wrote:
>For once, that doesn't seem to be the issue here. The bug only seems to happen
>on arm64 and doesn't reproduce on x86_64 hardware.
>
>> x <- as.numeric("-177253333.333333343267441")
>> sprintf("%.15f", x)
>[1] "-177253333.333333373069763"
>
>This is the number adjacent to -177253333.333333343267441 in IEEE 754.
>
>> writeBin(x, raw(8))
>[1] ac aa aa aa 57 21 a5 c1
>
>If you look at the hexadecimal representation, the least significant bit
>appears to be off by one: the first byte should be 0xAB rather than 0xAC
>(according to online calculators such as
>https://numeral-systems.com/ieee-754-converter/).
>
>Seems that decimal-to-float conversion has a bug on arm64. Note that I get the
>same result with
>
>> x <- -177253333.333333343267441
>
>so it's not specific to as.numeric().
>
>Best,
>Stephanie
>
>
>
>
>> On 9 Mar 2025, at 18:46, Jeff Newmiller via R-help <r-help@r-project.org>
>> wrote:
>>
>> https://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
>>
>> https://0.30000000000000004.com/
>>
>> On March 9, 2025 10:12:47 AM PDT, Christofer Bogaso
>> <bogaso.christo...@gmail.com> wrote:
>>> Hi,
>>>
>>> I have below simple conversion
>>>
>>>> sprintf("%0.15f", as.numeric("-177253333.333333343267441"))
>>>
>>> [1] "-177253333.333333373069763"
>>>
>>> I could not figure out why the input and output is different?
>>>
>>> Clearly this conversion is incorrect. Is there any way to convert to
>>> numerical properly?
>>>
>>>> sessionInfo()
>>>
>>> R version 4.4.0 (2024-04-24)
>>>
>>> Platform: aarch64-apple-darwin20
>>>
>>> Running under: macOS 15.3.1
>>>
>>>
>>> Matrix products: default
>>>
>>> BLAS:
>>> /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/lib/libRblas.0.dylib
>>>
>>> LAPACK:
>>> /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/lib/libRlapack.dylib;
>>> LAPACK version 3.12.0
>>>
>>>
>>> locale:
>>>
>>> [1] C/UTF-8/C/C/C/C
>>>
>>>
>>> time zone: Asia
>>>
>>> tzcode source: internal
>>>
>>>
>>> attached base packages:
>>>
>>> [1] stats graphics grDevices utils datasets methods base
>>>
>>>
>>> loaded via a namespace (and not attached):
>>>
>>> [1] compiler_4.4.0
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> https://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Sent from my phone. Please excuse my brevity.
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
--
Sent from my phone. Please excuse my brevity.
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
