Deal with random numbers outside target interval.

The zufall() ("coincidence," "random chance") function gets a random double
in the half-open interval [0, 1), and scales it to fall in the half-open
interval [min, max).  It asserts that the result is in that interval.  But
rounding can throw an occasional spanner in the works, and produce e.g. a
value that's equal to max.  When that happens, just throw the dice again.

1 files changed, 9 insertions, 1 deletions

diff --git a/mgizapp/src/mkcls/general.cpp b/mgizapp/src/mkcls/general.cpp
index 927142e..5d8cccc 100644
--- a/mgizapp/src/mkcls/general.cpp
+++ b/mgizapp/src/mkcls/general.cpp
@@ -97,7 +97,15 @@ double zufall01()
 
 double zufall(double min,double max)
 {
-  double z=zufall01()*(max-min)+min;
+  double z;
+  // Get a random double from 0 inclusive to 1 exclusive, and scale to fit
+  // the [min, max) interval.  In theory this always produces a number in the
+  // interval, but due to rounding errors it's possible occasionally to get
+  // something just outside it, especially z == max.  No point trying to
+  // optimize for that; we can just retry if it happens.
+  do {
+    z = zufall01()*(max-min)+min;
+  } while (z < min || z>= max);
   assert(z>=min&&z<max);
   return z;
 }