double HPL_dlamch( const HPL_T_MACH CMACH );
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).
- 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
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.
int main(int argc, char *argv)
eps = HPL_dlamch( HPL_MACH_EPS );
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).