Hi,
Could someone please explain how this impacts Pd's performance on the Raspberry Pi ? It doesn't make any sense to me right now, but i'm very curious...
Cheers,
Pierre.
2013/1/20 Hans-Christoph Steiner hans@at.or.at
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 floatingpoint 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
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