On 21/12/2021 20:46, Simon Urbanek wrote:
Matt,
yes, arm64 does not support long doubles. In C the long double type is 64-bit
there so has the same precision as doubles (this is allowed by the standard).
And documented in ?.Machine.
However, I see on my M1 Pro
capabilities("long.double")
long.double
FALSE
on all the arm64 builds I have installed, including the current CRAN
distribution (of 4.1.2) and that at mac.r-project.org (see below). So I
have no idea why TRUE is reported below (if this really was an arm64
build run on the M1 Pro).
R version 4.1.2 Patched (2021-12-16 r81394) -- "Bird Hippie"
...
> capabilities('long.double')
long.double
FALSE
Cheers,
Simon
On Dec 22, 2021, at 9:21 AM, Matthew Heun via R-SIG-Mac
<r-sig-mac@r-project.org> wrote:
All:
I'm seeing some test failures on a new M1 Pro machine that I do not see on my
Intel machine. I'm investigating whether the test failures are caused by
machine precision differences. On my M1 Pro machine, differences of large
numbers are greater than a specified tolerance. (On my Intel machine,
differences between the supposed same numbers are within tolerance.)
A small number of packages (and R itself) have needed tolerances
increased for checks on arm64.
The output of .Machine shows some differences. I have 2 questions below, each identified
by "****".
(1) For sizeof.longdouble, I see the following:
Intel machine:
$sizeof.longdouble
[1] 16
M1 Pro machine:
$sizeof.longdouble
[1] 8
?.Machine says:
sizeof.longdouble
the number of bytes in a C long double type. Will be zero if there is no such
type (or its use was disabled when R was built), otherwise possibly12 (most
32-bit builds) or 16 (most 64-bit builds).
The M1 Pro uses a 64-bit architecture. So this result is surprising to me.
Furthermore,
capabilities("long.double")
long.double
TRUE
So somebody thinks that long doubles are supported.
**** Is the difference in sizeof.longdouble between the Intel and M1
architectures expected?
(2) Also, my M1 Pro machine is missing additional fields (that the Intel
machine reports):
$longdouble.eps
[1] 1.084202e-19
$longdouble.neg.eps
[1] 5.421011e-20
$longdouble.digits
[1] 64
$longdouble.rounding
[1] 5
$longdouble.guard
[1] 0
$longdouble.ulp.digits
[1] -63
$longdouble.neg.ulp.digits
[1] -64
$longdouble.exponent
[1] 15
$longdouble.min.exp
[1] -16382
$longdouble.max.exp
[1] 16384
**** Is there a reason why the above entries are missing from the output of
.Machine on the M1 Pro machine?
My R installation is: 4.1.2 Patched (2021/12/16, r81394)
Any help will be appreciated.
Cheers,
Matt
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
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