On Thu, Mar 08, 2012 at 10:08:41PM +0200, Manu wrote: > I find myself really wishing for proper multiple return values almost every > day, particularly when I work with maths heavy code, and especially for > efficiently returning error codes in functions I'd rather not throw from. > Many maths-y functions return some sort of pair; intersections return (ray, > t) or something of that type. > I'm finding HEAPS of SIMD functions want to return pairs (unpacks in > particular): int4 (low, hight) = unpack(someShort8); > Currently I have to duplicate everyting: int4 low = > unpackLow(someShort8); int4 high = unpackHigh(someShort8); > I'm getting really sick of that, it feels so... last millennium. > > The point of 'proper' multiple return values is to return each value in > registers, in its own register type, using exactly the same register > assignment pattern as when passing args TO functions. > I don't think this causes any side effects to the ABI, since the arg > registers are already volatile across function calls in the first place. > It just means that the returned-to function can find its return > values already conveniently in an appropriate register, avoiding memory > access. > > People argue I should return a tuple, but this isn't really the same, it > has hidden implications that complicate the optimisation potential. For > instance, tuples have an implicit structure/memory layout which can't be > ignored, whereas return values don't have memory allocated, ie, you can't > take the address of a return value without first assigning it to some local > syntactically. [...]
Couldn't you just use ref parameters? Or does the compiler turn them into pointers? T -- The volume of a pizza of thickness a and radius z can be described by the following formula: pi zz a. -- Wouter Verhelst
