MACHINE is a FORTRAN90 library which returns machine constants, particularly those related to arithmetic with single precision real and double precision real quantities.
In FORTRAN90, there are built-in arithmetic functions that can immediately return the values that MACHINE is supposed to have stored. You should prefer to use the values supplied by FORTRAN90, since these will automatically be adjusted to the appropriate values for the computer you are using, and the arithmetic precision you have chosen!
If X is a single precision real value,then:
If X is a double precision real value, then:
MACHINE is not an "intelligent" program; it's simply a way to store and retrieve the information necessary to describe the arithmetic performed on a given computer. Therefore, if you plan to use MACHINE on a particular kind of computer, you must verify that the values being returned are appropriate.
One way to do this is to run the program MACHAR which is an "intelligent" program that actually tries to determine machine arithmetic properties dynamically.
MACHINE uses some simple conventions to describe how integers and real numbers are stored on an arbitrary computer.
MACHINE assumes that integers are represented using S digits in base A:
Sign * ( X(S-1)*A^(S-1) + ... + X(1)*A + X(0))
MACHINE assumes that real numbers are represented using a mantissa T, base B and exponent E as:
Sign * T * BE
D1MACH returns quantities associated with double precision arithmetic, including:
I1MACH returns quantities associated with integer arithmetic, as well as some integer quantities associated with real and double precision arithmetic, and other machine-specific information.
R1MACH returns quantities associated with single precision arithmetic, including:
MACHINE is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version and a Python version.
F90, FORTRAN90 programs which tests the routines, EPSILON, HUGE, and TINY for evaluating some machine arithmetic quantities directly.
MACHAR, a FORTRAN90 library which can compute machine arithmetic quantities dynamically.
NMS, a FORTRAN90 library which includes MACHINE.
SLATEC, a FORTRAN90 library which includes MACHINE.
You can go up one level to the FORTRAN90 source codes.