[PD-dev] d_math.c "break[s] strict-aliasing rules"
Hans-Christoph Steiner
hans at eds.org
Wed Apr 18 17:19:20 CEST 2007
So it seems that this bug in d_math.c is triggered by turning on the
Apple-recommended optimization flags:
http://sourceforge.net/tracker/index.php?
func=detail&aid=1692649&group_id=55736&atid=478070
I did notice that there are these warnings in the source. IIRC,
optimization generally requires strict aliasing, so it seems that
these warnings are probably related to the above bug:
d_math.c: In function 'init_rsqrt':
d_math.c:79: warning: dereferencing type-punned pointer will break
strict-aliasing rules
d_math.c: In function 'q8_rsqrt':
d_math.c:93: warning: dereferencing type-punned pointer will break
strict-aliasing rules
d_math.c: In function 'q8_sqrt':
d_math.c:101: warning: dereferencing type-punned pointer will break
strict-aliasing rules
Here are the lines in question:
79: *(long *)(&f) = l;
93: long l = *(long *)(&f);
101: long l = *(long *)(&f);
Can anyone speak to what's this for and what it can be replaced with
so as to follow "strict-aliasing rules". Maybe we could use
something like this instead (from http://www.cs.tut.fi/~jkorpela/
round.html ):
#define round(x) ((x) < LONG_MIN-0.5 || (x) > LONG_MAX+0.5 ?\
error() : ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))
This requires that you have #include <limits.h> and that you have an
error handling routine called error which is a function of type long.
.hc
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