HPL_dlamch(3)

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).