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.)
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
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