dlamch.c

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#include "f2c.h"

doublereal dlamch_(char *cmach)
{
/*  -- LAPACK auxiliary routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       October 31, 1992   


    Purpose   
    =======   

    DLAMCH determines double precision machine parameters.   

    Arguments   
    =========   

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

   ===================================================================== 
*/
/* >>Start of File<<   
       Initialized data */
    static logical first = TRUE_;
    /* System generated locals */
    integer i__1;
    doublereal ret_val;
    /* Builtin functions */
    double pow_di(doublereal *, integer *);
    /* Local variables */
    static doublereal base;
    static integer beta;
    static doublereal emin, prec, emax;
    static integer imin, imax;
    static logical lrnd;
    static doublereal rmin, rmax, t, rmach;
    extern logical lsame_(char *, char *);
    static doublereal small, sfmin;
    extern /* Subroutine */ int dlamc2_(integer *, integer *, logical *, 
	    doublereal *, integer *, doublereal *, integer *, doublereal *);
    static integer it;
    static doublereal rnd, eps;



    if (first) {
	first = FALSE_;
	dlamc2_(&beta, &it, &lrnd, &eps, &imin, &rmin, &imax, &rmax);
	base = (doublereal) beta;
	t = (doublereal) it;
	if (lrnd) {
	    rnd = 1.;
	    i__1 = 1 - it;
	    eps = pow_di(&base, &i__1) / 2;
	} else {
	    rnd = 0.;
	    i__1 = 1 - it;
	    eps = pow_di(&base, &i__1);
	}
	prec = eps * base;
	emin = (doublereal) imin;
	emax = (doublereal) imax;
	sfmin = rmin;
	small = 1. / rmax;
	if (small >= sfmin) {

/*           Use SMALL plus a bit, to avoid the possibility of rou
nding   
             causing overflow when computing  1/sfmin. */

	    sfmin = small * (eps + 1.);
	}
    }

    if (lsame_(cmach, "E")) {
	rmach = eps;
    } else if (lsame_(cmach, "S")) {
	rmach = sfmin;
    } else if (lsame_(cmach, "B")) {
	rmach = base;
    } else if (lsame_(cmach, "P")) {
	rmach = prec;
    } else if (lsame_(cmach, "N")) {
	rmach = t;
    } else if (lsame_(cmach, "R")) {
	rmach = rnd;
    } else if (lsame_(cmach, "M")) {
	rmach = emin;
    } else if (lsame_(cmach, "U")) {
	rmach = rmin;
    } else if (lsame_(cmach, "L")) {
	rmach = emax;
    } else if (lsame_(cmach, "O")) {
	rmach = rmax;
    }

    ret_val = rmach;
    return ret_val;

/*     End of DLAMCH */

} /* dlamch_ */

#include "f2c.h"

/* Subroutine */ int dlamc1_(integer *beta, integer *t, logical *rnd, logical 
	*ieee1)
{
/*  -- LAPACK auxiliary routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       October 31, 1992   


    Purpose   
    =======   

    DLAMC1 determines the machine parameters given by BETA, T, RND, and   
    IEEE1.   

    Arguments   
    =========   

    BETA    (output) INTEGER   
            The base of the machine.   

    T       (output) INTEGER   
            The number of ( BETA ) digits in the mantissa.   

    RND     (output) LOGICAL   
            Specifies whether proper rounding  ( RND = .TRUE. )  or   
            chopping  ( RND = .FALSE. )  occurs in addition. This may not 
  
            be a reliable guide to the way in which the machine performs 
  
            its arithmetic.   

    IEEE1   (output) LOGICAL   
            Specifies whether rounding appears to be done in the IEEE   
            'round to nearest' style.   

    Further Details   
    ===============   

    The routine is based on the routine  ENVRON  by Malcolm and   
    incorporates suggestions by Gentleman and Marovich. See   

       Malcolm M. A. (1972) Algorithms to reveal properties of   
          floating-point arithmetic. Comms. of the ACM, 15, 949-951.   

       Gentleman W. M. and Marovich S. B. (1974) More on algorithms   
          that reveal properties of floating point arithmetic units.   
          Comms. of the ACM, 17, 276-277.   

   ===================================================================== 
*/
    /* Initialized data */
    static logical first = TRUE_;
    /* System generated locals */
    doublereal d__1, d__2;
    /* Local variables */
    static logical lrnd;
    static doublereal a, b, c, f;
    static integer lbeta;
    static doublereal savec;
    extern doublereal dlamc3_(doublereal *, doublereal *);
    static logical lieee1;
    static doublereal t1, t2;
    static integer lt;
    static doublereal one, qtr;



    if (first) {
	first = FALSE_;
	one = 1.;

/*        LBETA,  LIEEE1,  LT and  LRND  are the  local values  of  BE
TA,   
          IEEE1, T and RND.   

          Throughout this routine  we use the function  DLAMC3  to ens
ure   
          that relevant values are  stored and not held in registers, 
 or   
          are not affected by optimizers.   

          Compute  a = 2.0**m  with the  smallest positive integer m s
uch   
          that   

             fl( a + 1.0 ) = a. */

	a = 1.;
	c = 1.;

/* +       WHILE( C.EQ.ONE )LOOP */
L10:
	if (c == one) {
	    a *= 2;
	    c = dlamc3_(&a, &one);
	    d__1 = -a;
	    c = dlamc3_(&c, &d__1);
	    goto L10;
	}
/* +       END WHILE   

          Now compute  b = 2.0**m  with the smallest positive integer 
m   
          such that   

             fl( a + b ) .gt. a. */

	b = 1.;
	c = dlamc3_(&a, &b);

/* +       WHILE( C.EQ.A )LOOP */
L20:
	if (c == a) {
	    b *= 2;
	    c = dlamc3_(&a, &b);
	    goto L20;
	}
/* +       END WHILE   

          Now compute the base.  a and c  are neighbouring floating po
int   
          numbers  in the  interval  ( beta**t, beta**( t + 1 ) )  and
 so   
          their difference is beta. Adding 0.25 to c is to ensure that
 it   
          is truncated to beta and not ( beta - 1 ). */

	qtr = one / 4;
	savec = c;
	d__1 = -a;
	c = dlamc3_(&c, &d__1);
	lbeta = (integer) (c + qtr);

/*        Now determine whether rounding or chopping occurs,  by addin
g a   
          bit  less  than  beta/2  and a  bit  more  than  beta/2  to 
 a. */

	b = (doublereal) lbeta;
	d__1 = b / 2;
	d__2 = -b / 100;
	f = dlamc3_(&d__1, &d__2);
	c = dlamc3_(&f, &a);
	if (c == a) {
	    lrnd = TRUE_;
	} else {
	    lrnd = FALSE_;
	}
	d__1 = b / 2;
	d__2 = b / 100;
	f = dlamc3_(&d__1, &d__2);
	c = dlamc3_(&f, &a);
	if (lrnd && c == a) {
	    lrnd = FALSE_;
	}

/*        Try and decide whether rounding is done in the  IEEE  'round
 to   
          nearest' style. B/2 is half a unit in the last place of the 
two   
          numbers A and SAVEC. Furthermore, A is even, i.e. has last  
bit   
          zero, and SAVEC is odd. Thus adding B/2 to A should not  cha
nge   
          A, but adding B/2 to SAVEC should change SAVEC. */

	d__1 = b / 2;
	t1 = dlamc3_(&d__1, &a);
	d__1 = b / 2;
	t2 = dlamc3_(&d__1, &savec);
	lieee1 = t1 == a && t2 > savec && lrnd;

/*        Now find  the  mantissa, t.  It should  be the  integer part
 of   
          log to the base beta of a,  however it is safer to determine
  t   
          by powering.  So we find t as the smallest positive integer 
for   
          which   

             fl( beta**t + 1.0 ) = 1.0. */

	lt = 0;
	a = 1.;
	c = 1.;

/* +       WHILE( C.EQ.ONE )LOOP */
L30:
	if (c == one) {
	    ++lt;
	    a *= lbeta;
	    c = dlamc3_(&a, &one);
	    d__1 = -a;
	    c = dlamc3_(&c, &d__1);
	    goto L30;
	}
/* +       END WHILE */

    }

    *beta = lbeta;
    *t = lt;
    *rnd = lrnd;
    *ieee1 = lieee1;
    return 0;

/*     End of DLAMC1 */

} /* dlamc1_ */

#include "f2c.h"

/* Subroutine */ int dlamc2_(integer *beta, integer *t, logical *rnd, 
	doublereal *eps, integer *emin, doublereal *rmin, integer *emax, 
	doublereal *rmax)
{
/*  -- LAPACK auxiliary routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       October 31, 1992   


    Purpose   
    =======   

    DLAMC2 determines the machine parameters specified in its argument   
    list.   

    Arguments   
    =========   

    BETA    (output) INTEGER   
            The base of the machine.   

    T       (output) INTEGER   
            The number of ( BETA ) digits in the mantissa.   

    RND     (output) LOGICAL   
            Specifies whether proper rounding  ( RND = .TRUE. )  or   
            chopping  ( RND = .FALSE. )  occurs in addition. This may not 
  
            be a reliable guide to the way in which the machine performs 
  
            its arithmetic.   

    EPS     (output) DOUBLE PRECISION   
            The smallest positive number such that   

               fl( 1.0 - EPS ) .LT. 1.0,   

            where fl denotes the computed value.   

    EMIN    (output) INTEGER   
            The minimum exponent before (gradual) underflow occurs.   

    RMIN    (output) DOUBLE PRECISION   
            The smallest normalized number for the machine, given by   
            BASE**( EMIN - 1 ), where  BASE  is the floating point value 
  
            of BETA.   

    EMAX    (output) INTEGER   
            The maximum exponent before overflow occurs.   

    RMAX    (output) DOUBLE PRECISION   
            The largest positive number for the machine, given by   
            BASE**EMAX * ( 1 - EPS ), where  BASE  is the floating point 
  
            value of BETA.   

    Further Details   
    ===============   

    The computation of  EPS  is based on a routine PARANOIA by   
    W. Kahan of the University of California at Berkeley.   

   ===================================================================== 
*/
    /* Table of constant values */
    static integer c__1 = 1;
    
    /* Initialized data */
    static logical first = TRUE_;
    static logical iwarn = FALSE_;
    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2, d__3, d__4, d__5;
    /* Builtin functions */
    double pow_di(doublereal *, integer *);
    /* Local variables */
    static logical ieee;
    static doublereal half;
    static logical lrnd;
    static doublereal leps, zero, a, b, c;
    static integer i, lbeta;
    static doublereal rbase;
    static integer lemin, lemax, gnmin;
    static doublereal small;
    static integer gpmin;
    static doublereal third, lrmin, lrmax, sixth;
    extern /* Subroutine */ int dlamc1_(integer *, integer *, logical *, 
	    logical *);
    extern doublereal dlamc3_(doublereal *, doublereal *);
    static logical lieee1;
    extern /* Subroutine */ int dlamc4_(integer *, doublereal *, integer *), 
	    dlamc5_(integer *, integer *, integer *, logical *, integer *, 
	    doublereal *);
    static integer lt, ngnmin, ngpmin;
    static doublereal one, two;



    if (first) {
	first = FALSE_;
	zero = 0.;
	one = 1.;
	two = 2.;

/*        LBETA, LT, LRND, LEPS, LEMIN and LRMIN  are the local values
 of   
          BETA, T, RND, EPS, EMIN and RMIN.   

          Throughout this routine  we use the function  DLAMC3  to ens
ure   
          that relevant values are stored  and not held in registers, 
 or   
          are not affected by optimizers.   

          DLAMC1 returns the parameters  LBETA, LT, LRND and LIEEE1. 
*/

	dlamc1_(&lbeta, &lt, &lrnd, &lieee1);

/*        Start to find EPS. */

	b = (doublereal) lbeta;
	i__1 = -lt;
	a = pow_di(&b, &i__1);
	leps = a;

/*        Try some tricks to see whether or not this is the correct  E
PS. */

	b = two / 3;
	half = one / 2;
	d__1 = -half;