Hi, .... >> + >> +/* generate a mask that covers 1024 interrupts with <b> bits per IRQ */ >> +#define VGIC_ADDR_IRQ_MASK(b) GENMASK_ULL(ilog2(b) + ilog2(1024) - \ >> + ilog2(BITS_PER_BYTE) - 1, 0) >> +#define VGIC_ADDR_TO_INTID(addr, bits) (((addr) & VGIC_ADDR_IRQ_MASK(bits)) * \ >> + 64 / (bits) / 8) > > In the comment we end up adding here, can we also describe why > (addr & <magic mask>) * <magic 64> / (bits) / <BITS_PER_BYTE OR BYTES_PER_ULL> > gives us what we need, because I don't get it. The reason is: we deal with 8 bits per byte, but have bits-per-interrupts values bigger than 8. Doing the maths in floating point arithmetic would work fine: (float)(addr & mask) * (8.0 / bits_per_IRQ) So would this comment make sense? /* * Since we can have more than 8 bits per interrupt, we can't use * "8 / bpi" as a multiplicand directly, so we use a * fixed-point-arithmetic version of it tailored to cover at most 64 * bits per IRQ. */ Cheers, Andre. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
