gegl:multiply (and divide etc) do not always properly process the aux == NULL case
On my laptop running (with multi.xml)
$GEGL_THREAD=1 gegl -o tmp.ppm -i multi.xml
produces a different output than
$GEGL_THREAD=4 gegl -o tmp.ppm -i multi.xml
The problem is the different chunk size, with 1 thread gegl:multiply processes few chunks entirely outside "aux" bounding box and so it receives a NULL aux
pointer, executing so
the value
branch and value's default (1.0) does not match the buffer abyss.
A quick hack is to set value = 0.0;
when gegl_operation_get_source_node (op, "aux")
does not return a NULL pointer.