MobileRead Forums - View Single Post

knc1 · 07-17-2012, 01:51 PM

The one (working) FFT example from yesterday was written when "ARM doesn't have hardware floating point".

Our Kindles do have hardware floating point, almost, sort-of, ...
The K3 (VFP) unit **almost** supports IEEE 754 except for a few of the details that don't matter in the simple math world used here.

While re-vamping that decade old code (whose big claim to fame at the moment is that it "works out of the box") a person would want to keep in mind at least the basics:
http://infocenter.arm.com/help/index.../Chdidbba.html
(and the topic just above on the left)
That the VFP does best with short vectors of 8 single or 4 double precision values.

Also note, because of the **almost** IEEE 754, you want to include in the gcc optons:
-mfpu=vfp -mfloat-abi=softfp -funsafe-math-optimizations -std=c99
Also that libm is a double precision library (the -std=c99 is for some libm functions).

07-17-2012, 01:51 PM	#34
knc1 Going Viral Posts: 17,212 Karma: 18210809 Join Date: Feb 2012 Location: Central Texas Device: No K1, PW2, KV, KOA	The one (working) FFT example from yesterday was written when "ARM doesn't have hardware floating point". Our Kindles do have hardware floating point, almost, sort-of, ... The K3 (VFP) unit almost supports IEEE 754 except for a few of the details that don't matter in the simple math world used here. While re-vamping that decade old code (whose big claim to fame at the moment is that it "works out of the box") a person would want to keep in mind at least the basics: http://infocenter.arm.com/help/index.../Chdidbba.html (and the topic just above on the left) That the VFP does best with short vectors of 8 single or 4 double precision values. Also note, because of the almost IEEE 754, you want to include in the gcc optons: -mfpu=vfp -mfloat-abi=softfp -funsafe-math-optimizations -std=c99 Also that libm is a double precision library (the -std=c99 is for some libm functions). Last edited by knc1; 07-17-2012 at 02:28 PM.