On Mon, Oct 18, 2021 at 09:35:41AM +0200, Morten Brørup wrote: > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Georg Sauthoff > > Sent: Sunday, 17 October 2021 22.37 > > +Ferruh, as delegate to v1 in Patchwork. > > > > > That means a superfluous cast is removed and aliasing through a uint8_t > > pointer is eliminated. NB: The C standard specifies that a unsigned > > char > > pointer may alias while the C standard doesn't include such requirement > > for uint8_t pointers. > > > > Also simplified the loop since a modern C compiler can speed up (i.e. > > auto-vectorize) it in a similar way. For example, GCC auto-vectorizes > > it > > for Haswell using AVX registers while halving the number of > > instructions > > in the generated code. > > > > Signed-off-by: Georg Sauthoff <m...@gms.tf> > > --- > > lib/net/rte_ip.h | 27 ++++++++------------------- > > 1 file changed, 8 insertions(+), 19 deletions(-) > > > > diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h > > index 05948b69b7..1b8c6519a9 100644 > > --- a/lib/net/rte_ip.h > > +++ b/lib/net/rte_ip.h > > @@ -141,29 +141,18 @@ rte_ipv4_hdr_len(const struct rte_ipv4_hdr > > *ipv4_hdr) > > static inline uint32_t > > __rte_raw_cksum(const void *buf, size_t len, uint32_t sum) > > { > > - /* workaround gcc strict-aliasing warning */ > > - uintptr_t ptr = (uintptr_t)buf; > > + /* extend strict-aliasing rules */ > > typedef uint16_t __attribute__((__may_alias__)) u16_p; > > - const u16_p *u16_buf = (const u16_p *)ptr; > > - > > - while (len >= (sizeof(*u16_buf) * 4)) { > > - sum += u16_buf[0]; > > - sum += u16_buf[1]; > > - sum += u16_buf[2]; > > - sum += u16_buf[3]; > > - len -= sizeof(*u16_buf) * 4; > > - u16_buf += 4; > > - } > > - while (len >= sizeof(*u16_buf)) { > > + const u16_p *u16_buf = (const u16_p *)buf; > > + const u16_p *end = u16_buf + len / sizeof(*u16_buf); > > + > > + for (; u16_buf != end; ++u16_buf) > > sum += *u16_buf; > > - len -= sizeof(*u16_buf); > > - u16_buf += 1; > > - } > > > > - /* if length is in odd bytes */ > > - if (len == 1) { > > + /* if length is odd, keeping it byte order independent */ > > + if (unlikely(len % 2)) { > > uint16_t left = 0; > > - *(uint8_t *)&left = *(const uint8_t *)u16_buf; > > + *(unsigned char*)&left = *(const unsigned char *)end; > > sum += left; > > } > > > > -- > > 2.31.1 > > > > Great work documenting your thoughts behind this patch, Georg! I, for one, > didn't know about the aliasing difference between uint8_t and unsigned char. > :-) > > After taking a good look at v2 and the Godbolt reference to confirm the > claimed benefits, there can be no doubts about this patch.
+1, thanks for the good documentation > Reviewed-by: Morten Brørup <m...@smartsharesystems.com> Acked-by: Olivier Matz <olivier.m...@6wind.com>
