The R Project SVN R

/*

 *  R : A Computer Language for Statistical Data Analysis

 *  Copyright (C) 1997--2018  The R Core Team

 *  Copyright (C) 2002--2009  The R Foundation

 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; either version 2 of the License, or

 *  (at your option) any later version.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, a copy is available at

 *  https://www.R-project.org/Licenses/

 */

#ifdef HAVE_CONFIG_H

# include <config.h>

#endif

#include <Defn.h>

#include <float.h>  /* for DBL_MAX */

#include <Graphics.h>

#include <Print.h>

#include <Rmath.h> // for Rexp10, imax2

/* used in graphics and grid */

SEXP CreateAtVector(double *axp, double *usr, int nint, Rboolean logflag)

{

/*	Create an  'at = ...' vector for  axis(.)

 *	i.e., the vector of tick mark locations,

 *	when none has been specified (= default).

 *

 *	axp[0:2] = (x1, x2, nInt), where x1..x2 are the extreme tick marks

 *		   {unless in log case, where nInt \in {1,2,3 ; -1,-2,....}

 *		    and the `nint' argument is used *instead*.}

 *	The resulting REAL vector must have length >= 1, ideally >= 2

 */

    SEXP at = R_NilValue;/* -Wall*/

    double umin, umax, dn, rng, small;

    int i, n, ne;

    if (!logflag || axp[2] < 0) { /* --- linear axis --- Only use axp[] arg. */

	n = (int)(fabs(axp[2]) + 0.25);/* >= 0 */

	dn = imax2(1, n);

	rng = axp[1] - axp[0];

	small = fabs(rng)/(100.*dn);

	at = allocVector(REALSXP, n + 1);

	for (i = 0; i <= n; i++) {

	    REAL(at)[i] = axp[0] + (i / dn) * rng;

	    if (fabs(REAL(at)[i]) < small)

		REAL(at)[i] = 0;

	}

    }

    else { /* ------ log axis ----- */

	Rboolean reversed = FALSE;

	n = (int)(axp[2] + 0.5);

	/* {xy}axp[2] for 'log': GLpretty() [./graphics.c] sets

	   n < 0: very small scale ==> linear axis, above, or

	   n = 1,2,3.  see switch() below */

	umin = usr[0];

	umax = usr[1];

	if (umin > umax) {

	    reversed = (axp[0] > axp[1]);

	    if (reversed) {

		/* have *reversed* log axis -- whereas

		 * the switch(n) { .. } below assumes *increasing* values

		 * --> reverse axis direction here, and reverse back at end */

		umin = usr[1];

		umax = usr[0];

		dn = axp[0]; axp[0] = axp[1]; axp[1] = dn;

	    }

	    else {

		/* can the following still happen... ? */

		warning("CreateAtVector \"log\"(from axis()): "

			"usr[0] = %g > %g = usr[1] !", umin, umax);

	    }

	}

	/* allow a fuzz since we will do things like 0.2*dn >= umin */

	umin *= 1 - 1e-12;

	umax *= 1 + 1e-12;

	dn = axp[0];

	if (dn < DBL_MIN) {/* was 1e-300; now seems too cautious */

	    if (dn <= 0) /* real trouble (once for Solaris) later on */

		error("CreateAtVector [log-axis()]: axp[0] = %g < 0!", dn);

	    else

		warning("CreateAtVector [log-axis()]: small axp[0] = %g", dn);

	}

	/* You get the 3 cases below by

	 *  for (y in 1e-5*c(1,2,8))  plot(y, log = "y")

	 */

	switch(n) {

	case 1: /* large range:	1	 * 10^k */

	    i = (int)(floor(log10(axp[1])) - ceil(log10(axp[0])) + 0.25);

	    ne = i / nint + 1;

#ifdef DEBUG_axis

	    REprintf("CreateAtVector [log-axis(), case 1]: (nint, ne) = (%d,%d)\n",

		     nint, ne);

#endif

	    if (ne < 1)

		error("log - axis(), 'at' creation, _LARGE_ range: "

		      "ne = %d <= 0 !!\n"

		      "\t axp[0:1]=(%g,%g) ==> i = %d;	nint = %d",

		      ne, axp[0],axp[1], i, nint);

	    rng = Rexp10((double)ne); /* >= 10 */

	    n = 0;

	    while (dn < umax) {

		n++;

		dn *= rng;

	    }

	    if (!n)

		error("log - axis(), 'at' creation, _LARGE_ range: "

		      "invalid {xy}axp or par; nint=%d\n"

		      "	 axp[0:1]=(%g,%g), usr[0:1]=(%g,%g); i=%d, ni=%d",

		      nint, axp[0],axp[1], umin,umax, i,ne);

	    at = allocVector(REALSXP, n);

	    dn = axp[0];

	    n = 0;

	    while (dn < umax) {

		REAL(at)[n++] = dn;

		dn *= rng;

	    }

	    break;

	case 2: /* medium range:  1, 5	  * 10^k */

	    n = 0;

	    if (0.5 * dn >= umin) n++;

	    for (;;) {

		if (dn > umax) break;

		n++;

		if (5 * dn > umax) break;

		n++;

		dn *= 10;

	    }

	    if (!n)

		error("log - axis(), 'at' creation, _MEDIUM_ range: "

		      "invalid {xy}axp or par;\n"

		      "	 axp[0]= %g, usr[0:1]=(%g,%g)",

		      axp[0], umin,umax);

	    at = allocVector(REALSXP, n);

	    dn = axp[0];

	    n = 0;

	    if (0.5 * dn >= umin) REAL(at)[n++] = 0.5 * dn;

	    for (;;) {

		if (dn > umax) break;		REAL(at)[n++] = dn;

		if (5 * dn > umax) break;	REAL(at)[n++] = 5 * dn;

		dn *= 10;

	    }

	    break;

	case 3: /* small range:	 1,2,5,10 * 10^k */

	    n = 0;

	    if (0.2 * dn >= umin) n++;

	    if (0.5 * dn >= umin) n++;

	    for (;;) {

		if (dn > umax) break;

		n++;

		if (2 * dn > umax) break;

		n++;

		if (5 * dn > umax) break;

		n++;

		dn *= 10;

	    }

	    if (!n)

		error("log - axis(), 'at' creation, _SMALL_ range: "

		      "invalid {xy}axp or par;\n"

		      "	 axp[0]= %g, usr[0:1]=(%g,%g)",

		      axp[0], umin,umax);

	    at = allocVector(REALSXP, n);

	    dn = axp[0];

	    n = 0;

	    if (0.2 * dn >= umin) REAL(at)[n++] = 0.2 * dn;

	    if (0.5 * dn >= umin) REAL(at)[n++] = 0.5 * dn;

	    for (;;) {

		if (dn > umax) break;		REAL(at)[n++] = dn;

		if (2 * dn > umax) break;	REAL(at)[n++] = 2 * dn;

		if (5 * dn > umax) break;	REAL(at)[n++] = 5 * dn;

		dn *= 10;

	    }

	    break;

	default:

	    error("log - axis(), 'at' creation: INVALID {xy}axp[3] = %g",

		  axp[2]);

	}

	if (reversed) {/* reverse back again - last assignment was at[n++]= . */

	    for (i = 0; i < n/2; i++) { /* swap( at[i], at[n-i-1] ) : */

		dn = REAL(at)[i];

		REAL(at)[i] = REAL(at)[n-i-1];

		REAL(at)[n-i-1] = dn;

	    }

	}

    } /* linear / log */

    return at;

}