[R-SIG-Mac] R install on silicon Mac lacks long.double capability

[Spencer Graves]

Naresh:


May I ask the application that requires long.double?


Might it make sense to revise the algorithm of the application to get 
enhanced precision without long.doubles?


EXAMPLE: Ordinary least squares regression to estimate b in Y = X b + e 
as b-hat = inverse(X'X) = X'Y. However, computing it that way discards 
half of the precision. To see that, we write X as its singular value 
decomposition UDV'. Then X'X = V D^2 V' and X'Y = V D Y. Then 
inverse(X'X) = inverse(V') inverse(D)^-2 inverse(V) %*% V D U' Y. If you 
compute that way, you throw away half of the precision of D. You can 
avoid that by computing inverse(V') inverse(D) U' Y.


This computation is more commonly done using the QR decomposition, where 
the loss of numeric precision is equivalent but not as obvious.


???
Please excuse if I have once again exposed my infinite ignorance. 
Spencer Graves


On 10/23/25 17:27, Simon Urbanek wrote:
> Naresh,
> 
> Both of those can only be FALSE by definition:
> 
> 1) arm64 hardware (Apple Silicon, i.e M1,2,3,4) has no support for long doubles, so you cannot enable that one.
> 
> 2) libxml is always FALSE since 4.2.0 - see ?capabilities:
> 
>    libxml: is there support for integrating ‘libxml’ with the R event loop?  ‘TRUE’ as from R 3.3.0, ‘FALSE’ as from R 4.2.0.
> 
> Cheers,
> Simon
> 
> PS: what you described in "My installation was in two steps” has no effect on R or its capabilities. Those steps are only required if you want to compile R yourself (or re-compile some packages).
> 
> 
>> On 24/10/2025, at 10:35 AM, Naresh Gurbuxani <naresh_gurbuxani using hotmail.com> wrote:
>>
>> On my new macbook pro, I installed R using package installer R-4.5.1-arm64.pkg
>> My installation lacks long.double and libxml capabilities.  How can these be enabled?
>>
>> My installation was in two steps:
>> 1.  Install Xcode developer tools (sudo xcode-select install), GNU fortran compiler (gfortran-14.2-universal.pkg at cran), gnu readline, liblzma, and pcre2 (using macports), texlive, and Xquartz.  Install R using above package installer.
>> 2.  Source install.R from https://mac.r-project.org/bin/.  In sudo R session, run install.libs("r-base-dev").  Reinstall R using above package installer.
>>
>>> capabilities()
>>        jpeg         png        tiff       tcltk         X11        aqua
>>        TRUE        TRUE        TRUE        TRUE        TRUE        TRUE
>>    http/ftp     sockets      libxml        fifo      cledit       iconv
>>        TRUE        TRUE       FALSE        TRUE        TRUE        TRUE
>>         NLS       Rprof     profmem       cairo         ICU long.double
>>        TRUE        TRUE        TRUE        TRUE        TRUE       FALSE
>>     libcurl
>>        TRUE
>>> sessionInfo()
>> R version 4.5.1 (2025-06-13)
>> Platform: aarch64-apple-darwin20
>> Running under: macOS Sequoia 15.4.1
>>
>> Matrix products: default
>> BLAS:   /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRblas.0.dylib
>> LAPACK: /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.12.1
>>
>> locale:
>> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
>>
>> time zone: America/New_York
>> tzcode source: internal
>>
>> attached base packages:
>> [1] stats     graphics  utils     datasets  grDevices methods   base
>>
>> other attached packages:
>> [1] latticeExtra_0.6-31 lattice_0.22-7      colorspace_2.1-2
>>
>> loaded via a namespace (and not attached):
>> [1] compiler_4.5.1     deldir_2.0-4       RColorBrewer_1.1-3 Rcpp_1.1.0
>> [5] interp_1.1-6       jpeg_0.1-11        grid_4.5.1         png_0.1-8
>>>
>>
>> nareshgurbuxani$ gfortran --version
>> GNU Fortran (GCC) 14.2.0
>> Copyright (C) 2024 Free Software Foundation, Inc.
>> This is free software; see the source for copying conditions.  There is NO
>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>
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>>
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