Miller, the vanilla Pd which can be installed from Raspbian with apt-get or Synaptic does have the subnormals problem, as can be checked with a test patch attached with my first post. When an input signal to [lop~] is shut off, CPU load increases substantially. Output values go down in the order of 1e-44, subnormal range. I was working on reverb algo's showing the same problem, and compiled with option -ffastmath / --fast-math to see if that would turn on RunFast mode, but it didn't.
I'm not familiar with ARM and it's coprocessors, but from Intel I do know that gcc doesn't implement certain specified optimization options (notably SSE versions) unless you also mention a processor type that can handle it . A similar case could be with Rpi's vfpv2; it can do RunFast mode but gcc doesn't implement it, until you find a way to specify vfpv2 (vfpv1 can't do RunFast). Miller, if you succeeded in getting automatic flush-to-zero on the Pi, it may be related to other flags which you've set. Arch flags which I've set so far are -march=armv6 and -mfpu=vfp. Option -mfpu=vfpv2 is not allowed. I would be happy to do further testing with compiler options, if you know some. The big-or-small checks are rather expensive for RPi, that's what I've found. Katja On Sun, Jan 20, 2013 at 8:24 PM, Miller Puckette <[email protected]> wrote: > Hi all... > > I think it's possible to get flush-to-zero behavior on the Pi (ARMv6) by > calling gcc with --fast-math. At any rate what I found was that, if I > compiled without --fast-math, when numbers got small (e.g., when a > reverberator decays down past 10^-38 or so), the patch would suddenly jump > in CPI usage as if it were trappnig to the kernel (as it does for i386). > But when I added --fast-math the problem went away. > > On i386 and x86_64, I believe that one can't get flush-to-zero (at least in > the "normal" non-SSE floating point instructions) so there's no choice but > to use a macro such as PD_BADFLOAT to protect against that. So in m_pd.h the > PD_BADFLOAT macro is only "turned on" for Intel. > > However I've been mistaken many times about all this in the past and won't > be surprised if I'm mistaken again. > > cheers > Miller > > On Sun, Jan 20, 2013 at 11:12:28AM -0500, Hans-Christoph Steiner wrote: >> >> I think this is what you want, from 'man gcc'. Its interesting to note that >> the NEON mode, which provides SIMD, also does not do denormals: >> >> -mfpu=name >> -mfpe=number >> -mfp=number >> This specifies what floating point hardware (or hardware emulation) is >> available on the target. Permissible names are: fpa, fpe2, fpe3, >> maverick, >> vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, >> neon, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16 and neon-vfpv4. -mfp and >> -mfpe are synonyms for -mfpu=fpenumber, for compatibility with older >> versions of GCC. >> >> If -msoft-float is specified this specifies the format of floating point >> values. >> >> If the selected floating-point hardware includes the NEON extension (e.g. >> -mfpu=neon), note that floating-point operations will not be used by >> GCC's >> auto-vectorization pass unless -funsafe-math-optimizations is also >> specified. This is because NEON hardware does not fully implement the >> IEEE >> 754 standard for floating-point arithmetic (in particular denormal values >> are treated as zero), so the use of NEON instructions may lead to a loss >> of >> precision. >> >> >> .hc >> >> On 01/20/2013 06:54 AM, katja wrote: >> > I was assuming, or maybe just hoping? that Raspberry Pi (and ARM >> > devices in general) would not suffer from Denormal's disease like >> > Intel processors do. But guess what: Pi's float coprocessor is IEEE >> > 754 compliant and does all denormals by default (can check with >> > attached denorm-test.pd). Bummer! As if one would use an ARM device to >> > calculate the size of a Majorana particle, rather than doing simple >> > dsp. Do we really need to enable PD-BIGORSMALL() checks for this poor >> > little processor? There seems to be something called 'RunFast mode' >> > for Pi's float processor vfpv2, but I see no way how to enable this >> > via gcc. Option -ffast-math is allowed but doesn't do the trick. Can't >> > find an option to set vfpv2 specifically, in gcc docs. >> > >> > Katja >> > >> > >> > >> > _______________________________________________ >> > [email protected] mailing list >> > UNSUBSCRIBE and account-management -> >> > http://lists.puredata.info/listinfo/pd-list >> > >> >> _______________________________________________ >> [email protected] mailing list >> UNSUBSCRIBE and account-management -> >> http://lists.puredata.info/listinfo/pd-list > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
