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#include <float.h>
#include <math.h>
#include <stdio.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;
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;
}
return rmach;
} /* end dmach */
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