Bug in logarithmic minitics + suggested fix

[Aapo L. <aap...@gm...>]

Hello everyone!

I found a bug in Gnuplot CVS logarithmic axis minitics in certain
user-controlled minitic settings when I was plotting a logarithmic graph
with rather long range today.  The following short script highlights the
problem:

set logscale y
set ytics 10
set mytics 10
plot [0:1e3] [1:1e10] x**3
pause -1
set ytics 100
set mytics 10
plot [0:1e3] [1:1e10] x**3
pause -1

The first plot has the minitics on the logarithmic y-axis as it should;
but the second plot with ytics having a longer step doesn't show any
minitics at all.  I think the 10 minitics should be there as ordered,
no?  So, I hurried through the Gnuplot CVS source and found a solution
(patch attached).  However, I'm not sure whether or not there are any
problems that I might have overlooked, so could someone who understands
the axis system check the problem and the patch, please?  Particularly,
I'm not sure why there was a (step <= 1.5) condition - I needed to
remove it to allow larger ytics steps than 1.5 (the example has step =
2.0).  As a bonus, the patch fixes a typo in comment, "but" should
probably be "bug".  :-)

Best Regards, and thanks for the good plotting program
Aapo Lankinen



--- src/axis.c  2006-07-10 19:32:44.000000000 +0300
+++ src/axis.c  2006-07-10 19:35:19.000000000 +0300
@@ -976,9 +976,9 @@
                    minitics = 0;       /* not much else we can do */
                else if (axis_array[axis].log) {
                    /* Sep 2005 - This case has been commented out since v3.7 */
-                   /* but in fact it seems correct, and fixes but #1223149 */
-                   ministart = ministep = step / minifreq * axis_array[axis].base;
-                   miniend = step * axis_array[axis].base;
+                   /* but in fact it seems correct, and fixes bug #1223149 */
+                   ministart = ministep = AXIS_UNDO_LOG(axis,step) / minifreq;
+                   miniend = AXIS_UNDO_LOG(axis,step);
                } else {
                    ministart = ministep = step / minifreq;
                    miniend = step;
@@ -1137,7 +1137,7 @@
                                             internal + mplace);
                    else
                        mtic = internal
-                           + (axis_array[axis].log && step <= 1.5
+                           + (axis_array[axis].log
                               ? AXIS_DO_LOG(axis,mplace)
                               : mplace);
                    if (inrange(mtic, internal_min, internal_max)