On 2025-03-09 5:55 p.m., Christofer Bogaso wrote:
So, based on the discussion points from the experts here, I understand
that this is an ARM specific problem.
However, what should I do for a solution?
I use ARM+R in my office workstation, so it may not be prudent to me
to just say ignore this problem and let Apple's Tim Cook take care of
it...
No, the problem is much deeper than that. If your work depends on
things that are way out in the limit of floating point precision, then
your work is unavoidably unstable already. The easiest way to fix this
is to avoid doing anything that depends on the 15th or 16th or higher
significant digit of what you are working with.
If you really need 20 or 30 digit precision, then you can do it in R,
but you need to be extra careful with every single calculation you're
doing. Base R calculations won't be good enough.
Duncan Murdoch
On Mon, Mar 10, 2025 at 1:01 AM Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote:
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
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______________________________________________
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--
Sent from my phone. Please excuse my brevity.
______________________________________________
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
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______________________________________________
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
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