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base (version 3.3)

.Machine: Numerical Characteristics of the Machine

Description

.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.

Usage

.Machine

Arguments

Value

A list with components
double.eps
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.
double.neg.eps
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.
double.xmin
the smallest non-zero normalized floating-point number, a power of the radix, i.e., double.base ^ double.min.exp. Normally 2.225074e-308.
double.xmax
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.
double.base
the radix for the floating-point representation: normally 2.
double.digits
the number of base digits in the floating-point significand: normally 53.
double.rounding
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.
double.guard
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.
double.ulp.digits
the largest negative integer i such that 1 + double.base ^ i != 1, except that it is bounded below by -(double.digits + 3). Normally -52.
double.neg.ulp.digits
the largest negative integer i such that 1 - double.base ^ i != 1, except that it is bounded below by -(double.digits + 3). Normally -53.
double.exponent
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.
double.min.exp
the largest in magnitude negative integer i such that double.base ^ i is positive and normalized. Normally -1022.
double.max.exp
the smallest positive power of double.base that overflows. Normally 1024.
integer.max
the largest integer which can be represented. Always $2^31 - 1 = 2147483647$.
sizeof.long
the number of bytes in a C long type: 4 or 8 (most 64-bit systems, but not Windows).
sizeof.longlong
the number of bytes in a C long long type. Will be zero if there is no such type, otherwise usually 8.
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 possibly 12 (most 32-bit builds) or 16 (most 64-bit builds).
sizeof.pointer
the number of bytes in a C SEXP type. Will be 4 on 32-bit builds and 8 on 64-bit builds of R.

Source

Uses a C translation of Fortran code in the reference, modified by the R Core Team to defeat over-optimization in recent compilers.

Details

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.

References

Cody, W. J. (1988) MACHAR: A subroutine to dynamically determine machine parameters. Transactions on Mathematical Software, 14, 4, 303--311.

See Also

.Platform for details of the platform.

Examples

Run this code
.Machine
## or for a neat printout
noquote(unlist(format(.Machine)))

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