/*! \file
Copyright (c) 2003, The Regents of the University of California, through
Lawrence Berkeley National Laboratory (subject to receipt of any required
approvals from U.S. Dept. of Energy)

All rights reserved.

The source code is distributed under BSD license, see the file License.txt
at the top-level directory.
*/
#include <float.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include "slu_ddefs.h"

double dmach(char *cmach)
{
/*  -- SuperLU auxiliary routine (version 5.0) --
    This uses C99 standard constants, and is thread safe.

    Must be compiled with -std=c99 flag.


    Purpose
    =======

    DMACH returns double precision machine parameters.

    Arguments
    =========

    CMACH   (input) CHARACTER*1
            Specifies the value to be returned by DMACH:
            = 'E' or 'e',   DMACH := eps
            = 'S' or 's ,   DMACH := sfmin
            = 'B' or 'b',   DMACH := base
            = 'P' or 'p',   DMACH := eps*base
            = 'N' or 'n',   DMACH := t
            = 'R' or 'r',   DMACH := rnd
            = 'M' or 'm',   DMACH := emin
            = 'U' or 'u',   DMACH := rmin
            = 'L' or 'l',   DMACH := emax
            = 'O' or 'o',   DMACH := rmax

            where

            eps   = relative machine precision
            sfmin = safe minimum, such that 1/sfmin does not overflow
            base  = base of the machine
            prec  = eps*base
            t     = number of (base) digits in the mantissa
            rnd   = 1.0 when rounding occurs in addition, 0.0 otherwise
            emin  = minimum exponent before (gradual) underflow
            rmin  = underflow threshold - base**(emin-1)
            emax  = largest exponent before overflow
            rmax  = overflow threshold  - (base**emax)*(1-eps)

   =====================================================================
*/

    double sfmin, small, rmach = 0.;

    if (strncmp(cmach, "E", 1)==0) {
	rmach = DBL_EPSILON * 0.5;
    } else if (strncmp(cmach, "S", 1)==0) {
	sfmin = DBL_MIN;
	small = 1. / DBL_MAX;
	if (small >= sfmin) {
	    /* Use SMALL plus a bit, to avoid the possibility of rounding
	       causing overflow when computing  1/sfmin. */
	    sfmin = small * (DBL_EPSILON*0.5 + 1.);
	}
	rmach = sfmin;
    } else if (strncmp(cmach, "B", 1)==0) {
	rmach = FLT_RADIX;
    } else if (strncmp(cmach, "P", 1)==0) {
	rmach = DBL_EPSILON * 0.5 * FLT_RADIX;
    } else if (strncmp(cmach, "N", 1)==0) {
	rmach = DBL_MANT_DIG;
    } else if (strncmp(cmach, "R", 1)==0) {
	rmach = FLT_ROUNDS;
    } else if (strncmp(cmach, "M", 1)==0) {
	rmach = DBL_MIN_EXP;
    } else if (strncmp(cmach, "U", 1)==0) {
	rmach = DBL_MIN;
    } else if (strncmp(cmach, "L", 1)==0) {
	rmach = DBL_MAX_EXP;
    } else if (strncmp(cmach, "O", 1)==0) {
	rmach = DBL_MAX;
    } else {
  ABORT("Not implemented.");
    }

    return rmach;

} /* end dmach */
