On 11/14/13 14:45, Antti Palosaari wrote: > On 11.11.2013 16:38, Hans Verkuil wrote: >> On 11/11/2013 03:19 PM, Andy Walls wrote: >>> On Sun, 2013-11-10 at 19:16 +0200, Antti Palosaari wrote: >>>> Convert unsigned 8 to float 32 [-1 to +1], which is commonly >>>> used format for baseband signals. >>> >>> Hi Annti, >>> >>> I don't think this a good idea. Floating point representations are >>> inherently non-portable. Even though most everything now uses IEEE-754 >>> representation, things like denormaliazed numbers may be treated >>> differently by different machines. If someone saves the data to a file, >>> endianess issues aside, there are no guarantees that a different machine >>> reading is going to interpret all the floating point data from that file >>> properly. >>> >>> I really would recommend staying with scaled integer representations or >>> explicit integer mantissa, exponent representations. >> >> For what it's worth: ALSA does support float format as well (both LE and BE). > > I want use existing data formats and that [-1 to +1] scaled 32-bit IEEE-754 floating point is de facto format for SDR application (actually pair of floats as a complex). > > Doing conversion inside libv4lconvert makes it very easy for write application. Currently I have implemented GNU Radio and SDRsharp plugins that feeds data from device via libv4l2 using mmap and conversion. > > Thanks to pointing endianess issue, I didn't though it all. I suspect those apps just relies to local endianess. So do I have to implement float format conversion with both endianess? I would say that it should be written with endianness conversion in mind. It's not likely to be used on a big-endian system, but it should be possible to support it without too much work. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
