.Machine is a variable holding information on the numerical
characteristics of the machine R is running on, such as the largest
double or integer and the machine's precision.
.MachineA list with components
the smallest positive floating-point number
x such that 1 + x != 1. It equals
double.base ^ ulp.digits if either double.base is 2 or
double.rounding is 0; otherwise, it is
(double.base ^ double.ulp.digits) / 2. Normally
2.220446e-16.
a small positive floating-point number x
such that 1 - x != 1. It equals
double.base ^ double.neg.ulp.digits if double.base is 2
or double.rounding is 0; otherwise, it is
(double.base ^ double.neg.ulp.digits) / 2. Normally
1.110223e-16. As double.neg.ulp.digits is bounded
below by -(double.digits + 3), double.neg.eps may not
be the smallest number that can alter 1 by subtraction.
the smallest non-zero normalized
floating-point number, a power of the radix, i.e.,
double.base ^ double.min.exp. Normally 2.225074e-308.
the largest normalized floating-point number.
Typically, it is equal to (1 - double.neg.eps) *
double.base ^ double.max.exp, but
on some machines it is only the second or third largest such
number, being too small by 1 or 2 units in the last digit of the
significand. Normally 1.797693e+308. Note that larger
unnormalized numbers can occur.
the radix for the floating-point representation:
normally 2.
the number of base digits in the floating-point
significand: normally 53.
the rounding action, one of
0 if floating-point addition chops;
1 if floating-point addition rounds, but not in the IEEE style;
2 if floating-point addition rounds in the IEEE style;
3 if floating-point addition chops, and there is partial underflow;
4 if floating-point addition rounds, but not in the IEEE style, and
there is partial underflow;
5 if floating-point addition rounds in the IEEE style, and there is
partial underflow.
Normally 5.
the number of guard digits for multiplication
with truncating arithmetic. It is 1 if floating-point arithmetic
truncates and more than double digits base-double.base digits
participate in the post-normalization shift of the floating-point
significand in multiplication, and 0 otherwise.
Normally 0.
the largest negative integer i such
that 1 + double.base ^ i != 1, except that it is bounded below by
-(double.digits + 3). Normally -52.
the largest negative integer i
such that 1 - double.base ^ i != 1, except that it is bounded
below by -(double.digits + 3). Normally -53.
the number of bits (decimal places if double.base is 10) reserved
for the representation of the exponent (including the bias or sign)
of a floating-point number. Normally 11.
the largest in magnitude negative integer i such that
double.base ^ i is positive and normalized. Normally -1022.
the smallest positive power of double.base that overflows. Normally
1024.
the largest integer which can be represented. Always \(2^31 - 1 = 2147483647\).
the number of bytes in a C long type:
4 or 8 (most 64-bit systems, but not Windows).
the number of bytes in a C long long
type. Will be zero if there is no such type, otherwise usually
8.
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 possibly
12 (most 32-bit builds) or 16 (most 64-bit builds).
the number of bytes in a C SEXP
type. Will be 4 on 32-bit builds and 8 on 64-bit
builds of R.
The algorithm is based on Cody's (1988) subroutine MACHAR. As all current implementations of R use 32-bit integers and use IEC 60559 floating-point (double precision) arithmetic, all but three of the last four values are the same for almost all R builds.
Note that on most platforms smaller positive values than
.Machine$double.xmin can occur. On a typical R platform the
smallest positive double is about 5e-324.
Cody, W. J. (1988) MACHAR: A subroutine to dynamically determine machine parameters. Transactions on Mathematical Software, 14, 4, 303--311.
.Platform for details of the platform.
.Machine
## or for a neat printout
noquote(unlist(format(.Machine)))
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