On Tue, Apr 07, 2020 at 05:51:54AM -0400, Jeffrey Walton wrote: > Hi Everyone, > > I'm porting a 64-bit algorithm to 32-bit PowerPC (an old PowerMac). > The algorithm is simple when 64-bit is available, but it gets a little > ugly under 32-bit. > > PowerPC has a "Vector Subtract Carryout Unsigned Word" (vsubcuw), > https://www.nxp.com/docs/en/reference-manual/ALTIVECPEM.pdf. The > altivec intrinsics are vec_vsubcuw and vec_subc. > > The problem is, I don't know how to use it. I've been experimenting > with it but I don't see the use (yet). > > How does one use vsubcuw to implement a subtract with borrow?
Does your 32 bit powerpc have altivec? A lot do not. It is certainly not a universal feature. As far as I remember, G4 and G5 powermacs have it, but nothing older. -- Len Sorensen
