plotscale.c

speech signal process tools

/*--------------------------------------------------------------+
| ENTROPIC PROCESSING, INC.					|
|								|
| This material contains proprietary software of Entropic	|
| Processing, Inc.  Any reproduction, distribution, or		|
| publication without the the prior written permission of	|
| Entropic Processing, Inc.  is strictly prohibited.  Any	|
| public distribution of copies of this work authorized in	|
| writing by Entropic Processing, Inc.  must bear the notice 	|
|								|
|          "Copyright 1986 Entropic Processing, Inc."           |
|								|
+---------------------------------------------------------------+
|								|
| plotscale -- find round numbers for plot boundaries.		|
|								|
| Joseph T. Buck, Entropic Processing, Inc.			|
+--------------------------------------------------------------*/
/*
Plotscale works as follows.  First it attempts to find a
divisor, as follows.  It computes log10 of the difference vmax -
vmin, or mindif, whichever is greater.  int (log10) is the
exponent.  Then it finds the divides through by 10^exp to find
the mantissa:  (1.0 <= mantissa < 10.0).  It finds the first
integer larger than the mantissa.  If it is two or three, the
divisor is 0.5*10^exp.  Otherwise it is 10^exp.  

The returned min and max are evenly divisible by this divisor;
*p_vmin is the floor, and *p_vmax is the ceiling.  Let
	nticks = (*p_vmax - *p_vmin) / divisor
then if nticks < 8, div is the tick spacing.  Otherwise, if
nticks is divisible by 3, 3*div is the spacing, otherwise 2*div
is the spacing.  *p_ndp is the number of places after the
decimal point (0 if the tick spacing is an integer.  
*/

#ifdef SCCS
	static char *sccs_id = "@(#)plotscale.c	1.2 9/23/86 EPI";
#endif
#include <stdio.h>
double pow (), log10 ();

void
plotscale (vmin, vmax, mindif, p_vmin, p_vmax, p_vtick, p_ndp)
double    vmin, vmax, mindif, *p_vmin, *p_vmax, *p_vtick;
int     *p_ndp;
{
    double   diff = vmax - vmin, teno, div, adiff;
    int     o, adj, nticks;
    if (diff < 0.0) diff = mindif;
    o = log10 (diff);
    teno = pow (10.0, (double) o);
    adj = diff / teno + 0.999;
    adiff = adj * teno;
    div = teno;
    if (adj <= 3)
	div = teno / 2;
/* Now move vmin down so it is divisible by div. */
    if (vmin >= 0.0)
	vmin = ((int) (vmin / div)) * div;
    else
	vmin = -((int) (-vmin / div + 0.9999)) * div;
/* Now move vmax up so it is divisible by div. */
    if (vmax >= 0.0)
	vmax = ((int) (vmax / div + 0.9999)) * div;
    else
	vmax = -((int) (-vmax / div)) * div;
    *p_vmin = vmin;
    *p_vmax = vmax;
/* Figure out tick marks. */
    adiff = vmax - vmin;
    nticks = adiff / div;
    if (nticks < 8)
	*p_vtick = div;
    else if (nticks % 3 == 0)
	*p_vtick = div * 3;
    else
	*p_vtick = div * 2;
    *p_ndp = 0;
    if (*p_vtick < 1.0)
	*p_ndp = 0.9999 - log10 (*p_vtick);
    return;
}