From 6daa69a032fb18c757b79338ccaba530a1540f02 Mon Sep 17 00:00:00 2001
From: oetiker <oetiker@a5681a0c-68f1-0310-ab6d-d61299d08faa>
Date: Fri, 16 May 2008 12:07:58 +0000
Subject: [PATCH] fix handling of values <= zero for logarithmic display

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1356 a5681a0c-68f1-0310-ab6d-d61299d08faa
---
 src/rrd_graph.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/rrd_graph.c b/src/rrd_graph.c
index eec7e45..37e97b8 100644
--- a/src/rrd_graph.c
+++ b/src/rrd_graph.c
@@ -1255,24 +1255,29 @@ int data_proc(
        lets set these to dummy values then ... */
 
     if (im->logarithmic) {
-        if (isnan(minval))
-            minval = 0.2;
-        if (isnan(maxval))
+        if (isnan(minval) || isnan(maxval) || maxval <= 0) {
+            minval = 0.0; /* catching this right away below */
             maxval = 5.1;
+        }
+        /* in logarithm mode, where minval is smaller or equal 
+           to 0 make the beast just way smaller than maxval */
+        if (minval <= 0) {
+            minval = maxval / 10e8;
+        }
     } else {
-        if (isnan(minval))
+        if (isnan(minval) || isnan(maxval)) {
             minval = 0.0;
-        if (isnan(maxval))
             maxval = 1.0;
+        }
     }
 
-    /* adjust min and max values */
+    /* adjust min and max values given by the user*/
     /* for logscale we add something on top */
     if (isnan(im->minval)
         || ((!im->rigid) && im->minval > minval)
         ) {
         if (im->logarithmic)
-            im->minval = minval * 0.5;
+            im->minval = minval / 2.0;
         else
             im->minval = minval;
     }
@@ -4277,7 +4282,7 @@ void rrd_graph_options(
         }
     }
 
-    if (im->logarithmic == 1 && im->minval <= 0) {
+    if (im->logarithmic && im->minval <= 0) {
         rrd_set_error
             ("for a logarithmic yaxis you must specify a lower-limit > 0");
         return;
-- 
2.11.0