# 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).