# Name

**HPL_dlamch** determines machine-specific arithmetic constants.
# Synopsis

`#include "hpl.h"`

`double`

`HPL_dlamch(`

`const HPL_T_MACH`

`CMACH`

`);`

# Description

**HPL_dlamch**
determines machine-specific arithmetic constants such as
the relative machine precision (eps), the safe minimum (sfmin) such
that 1 / sfmin does not overflow, the base of the machine (base), the
precision (prec), the number of (base) digits in the mantissa (t),
whether rounding occurs in addition (rnd=1.0 and 0.0 otherwise), the
minimum exponent before (gradual) underflow (emin), the underflow
threshold (rmin) base**(emin-1), the largest exponent before overflow
(emax), the overflow threshold (rmax) (base**emax)*(1-eps).
# Arguments

CMACH (local input) const HPL_T_MACH
Specifies the value to be returned by HPL_dlamch
= HPL_MACH_EPS, HPL_dlamch := eps (default)
= HPL_MACH_SFMIN, HPL_dlamch := sfmin
= HPL_MACH_BASE, HPL_dlamch := base
= HPL_MACH_PREC, HPL_dlamch := eps*base
= HPL_MACH_MLEN, HPL_dlamch := t
= HPL_MACH_RND, HPL_dlamch := rnd
= HPL_MACH_EMIN, HPL_dlamch := emin
= HPL_MACH_RMIN, HPL_dlamch := rmin
= HPL_MACH_EMAX, HPL_dlamch := emax
= HPL_MACH_RMAX, HPL_dlamch := rmax
where
eps = relative machine precision,
sfmin = safe minimum,
base = base of the machine,
prec = eps*base,
t = number of digits in the mantissa,
rnd = 1.0 if rounding occurs in addition,
emin = minimum exponent before underflow,
rmin = underflow threshold,
emax = largest exponent before overflow,
rmax = overflow threshold.

# Example

`#include "hpl.h"`

int main(int argc, char *argv[])
{
double eps;
eps = HPL_dlamch( HPL_MACH_EPS );
printf("eps=%18.8e\n", eps);
exit(0); return(0);
}

# References

This function has been manually translated from the Fortran 77 LAPACK
auxiliary function dlamch.f (version 2.0 -- 1992), that was itself
based on the function ENVRON by Malcolm and incorporated suggestions
by Gentleman and Marovich. See
Malcolm M. A., Algorithms to reveal properties of floating-point
arithmetic., Comms. of the ACM, 15, 949-951 (1972).
Gentleman W. M. and Marovich S. B., More on algorithms that reveal
properties of floating point arithmetic units., Comms. of the ACM,
17, 276-277 (1974).