On 26/03/2017 15:28, Artyom Beilis via Boost wrote:
Still do you have examples or documentation for:
How do I cast for example low part or high part something like:
pack<unsigned byte,16> v; pack<unsigned short,8> v1=cast_low(v); // note sometimes I indeed need only low or only high part - not both pack<unsigned short,8> v2=cast_high(v); ... v=join_cast(v1,v2); // short to byte
What is saturation policy: if I have unsigned short of value 257 casted to unsigned char would it cast to 1 or to 255? How can I control the policy?
If you only need part of it, it's not a cast, it's a split as cast preserve cardinality of pack. pack<unsigned byte,16> v; pack<unsigned short,8> v1=split_low(v); pack<unsigned short,8> v2=split_high(v); and if you need both : pack<unsigned byte,16> v; auto vs = split(v); and vs[0],vs[1] are the low and high parts respectively. IIRC split has no saturation policy as saturation is what we use when you go down the type. You can rebuild a smaller type using group or saturated_(group). You also have slice that slice a pack in two, keeping the type but reducing the cardinal. combine do the reverse. Considering this complexity, most of the common use-cases are handled by pack_cast already, leaving direct call to split_* for more advanced usages. As for the doc, thanks for raising an actual bug, the doc is not indeed properly included. Will fix this. Maybe a tutorial about pack_cast,slice,split,group and combine is indeed needed.