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).