Hi!
ARROW-3329 - we can discuss there.
> It seems like it makes sense to implement both lossless safe casts
> (when all zeros after the decimal point) and lossy casts (fractional
> part discarded) from decimal to integer, do I have that right?
Yes, though if I understood your examples are the same case - in both
cases fractional part is discarded - just it is all 0s in the first
case.
The key question is whether CastFunctor in cast.cc has access to scale
of the decimal? If yes how?
If not - these are the options I've came up with:
Let's assume Decimal128Type value is n
Then I expect that base call
.cast('int64') will return overflow for n beyond int64 values, value otherwise
Option 1:
.cast('int64', decimal_scale=s) would calculate n/10**s and return
overflow if it is beyond int64, value otherwise
Option 2:
.cast('int64', bytes_group=0) would return n & 0x00000000FFFFFFFF
.cast('int64', bytes_group=1) would return (n >> 64) & 0x00000000FFFFFFFF
.cast('int64') would have default value bytes_group=0
Option 3:
cast has no CastOptions but we add multiply compute kernel and have
something like this instead:
.compute('multiply', 10**-s).cast('int64')
BR,
Jacek
