On Wed, 27 Jun 2018 15:43:38 +0200 Mathieu Othacehe <m.othacehe@xxxxxxxxx> wrote: > Hi Jonathan, > > > https://en.wikipedia.org/wiki/Double-precision_floating-point_format. > > > > So in rough form... > > > > fls('mantissa') will get us the most significant set bit. > > Shift the mantissa so that falls off the top and add that shift > > to the exponent. > > > > Poke in the right places in a standard double. > > Yes, understood, this way we can format Intersil float representation > (m*2^e) to IEEE754 (1.m*2^e). > > > Now this is where it gets even uglier. IIO assumes 2 32 bit > > parts so we'll need to mash it into those in some reasonable > > (ish) fashion. The core IIO then needs to pretty print it. > > An option would be to add IIO_VAL_DOUBLE format value that would print > ieee754 double in a similar way as '%a' option of glibc' printf > ([-]0xh.hhhhp). It's not exactly human readable if we print it like that so not ideal. Hmm. It would be nice for reading it back into a program though. Perhaps put out a patch doing this as an RFC and we'll see what response we get! > > A "iio_double_to_int" function would also be needed to parse a user > inputed number under '%a' representation into two 'int' passed to > write_raw. yes - nasty but we'll need it. > > > Hmm. This looks annoyingly like we may need to do some core > > rework to make val and val2 64 bit relatively soon but I'd > > rather we didn't stall this driver on that. > > Yes the splitting would be really ugly as the mantissa on 52 bit will > have to be splitted in two parts, something like: > > val: sign | exponent | mantissa (20 most valuable bits) > val2: mantissa (32 last bits) > > Or something as dirty as that ... > > All of this seems really hacky but would allow user to input big > floating values (that won't fit into val.val2 format with val and val2 > on 32 or even 64 bit format). > > What do you think ? We can make it less hacky by adding a new callback function similar to we did for the quaternion case - read_raw_multi that at least takes 64 bit val and val2 so we can shove a double in one of them (without using floating point maths in kernel as that's a pain) Jonathan > > Thanks, > > Mathieu -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
