I was looking through the bhyve code and noticed an obvious easy (if trivial) code improvement.
Tested "standalone" rather than inside bhyve (with both gcc and clang, on FreeBSD 9.0). Not sure where/how diffs should go, so I figured I would send this here as a test. :-) Chris Index: pci_virtio_block.c =================================================================== --- pci_virtio_block.c (revision 247510) +++ pci_virtio_block.c (working copy) @@ -164,14 +164,19 @@ static int hq_num_avail(struct vring_hqueue *hq) { - int ndesc; + uint16_t ndesc; - if (*hq->hq_avail_idx >= hq->hq_cur_aidx) - ndesc = *hq->hq_avail_idx - hq->hq_cur_aidx; - else - ndesc = UINT16_MAX - hq->hq_cur_aidx + *hq->hq_avail_idx + 1; + /* + * We're just computing (a-b) in GF(2^16). + * + * The only glitch here is that in standard C, + * uint16_t promotes to (signed) int when int has + * more than 16 bits (pretty much always now), so + * we have to force it back to unsigned. + */ + ndesc = (unsigned)*hq->hq_avail_idx - (unsigned)hq->hq_cur_aidx; - assert(ndesc >= 0 && ndesc <= hq->hq_size); + assert(ndesc <= hq->hq_size); return (ndesc); } _______________________________________________ freebsd-virtualization@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to "freebsd-virtualization-unsubscr...@freebsd.org"