On 11/1/18 7:06 PM, dick balaska wrote:
> On 10/26/18 2:02 AM, clipka wrote:
> 
> Most humbly, I would like to point out that the Debian POV-Ray 3.7.0.x
> package does not use -ffast-math.  So, "usually" might be a bit strong.
> 
>  From debian/rules:
>    CXXFLAGS += -O3
> 
>    # This is rumoured to give wrong results with zero-thickness boxes, so
>    # disabled
>    # CXXFLAGS += -ffast-math
> 
> 
> and a compile line:
> g++ -DHAVE_CONFIG_H -I. -I..  -I.. -I../source/backend -I../source/base
> -I../source/frontend -I../unix -I../vfe -I../vfe/unix -I/usr/include/SDL
> -D_GNU_SOURCE=1 -D_REENTRANT -I/usr/include/OpenEXR -Wdate-time
> -D_FORTIFY_SOURCE=2 -pthread -I/usr/include  -I/usr/include  -pipe
> -Wno-multichar -Wno-write-strings -fno-enforce-eh-specs
> -Wno-non-template-friend -g -O2
> -fdebug-prefix-map=/home/dick/povray/debian/povray-3.7.0.7=.
> -fstack-protector-strong -Wformat -Werror=format-security -O3 -pthread
> -c -o lightgrp.o lightgrp.cpp
> 

Interesting. I see too -fstack-protector-strong which off the top of my 
head the default compile does not use. Oh, and there is no -march=native 
so expect quite a few other optimizations not done. -D_FORTIFY_SOURCE=2 
added too.

Suppose compile differences like these something to keep in mind when 
someone reports a bug or performance concern where they might be using a 
pre-compiled package with different defaults than POV-Ray 'publishes.'

Aside: I've never done comparisons with and without -ffast_math. Wonder 
what the performance (result?) difference is...

Aside: Zero thickness boxes I'd think problematic in any case. Not 
opaque, differing inside/outside textures etc. Perhaps to the point the 
parser should complain on seeing such a box. Maybe something else 
meant...

Bill P.

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