Re: [PATCH 03/24] checksum: align buffers

On Mon, 5 Feb 2024 17:02:00 +1100
David Gibson <david(a)gibson.dropbear.id.au> wrote:

...
  On Fri, Feb 02, 2024 at 03:11:30PM +0100, Laurent
Vivier wrote:
  if buffer is not aligned use sum_16b() only on
the not aligned
 part, and then use csum() on the remaining part
 
 Signed-off-by: Laurent Vivier <lvivier(a)redhat.com>   
 
 Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>
 
  ---
  checksum.c | 14 +++++++++++++-
  1 file changed, 13 insertions(+), 1 deletion(-)
 
 diff --git a/checksum.c b/checksum.c
 index f21c9b7a14d1..c94980771c63 100644
 --- a/checksum.c
 +++ b/checksum.c
 @@ -407,7 +407,19 @@ less_than_128_bytes:
  __attribute__((optimize("-fno-strict-aliasing")))	/* See csum_16b() */
  uint16_t csum(const void *buf, size_t len, uint32_t init)
  {
 -	return (uint16_t)~csum_fold(csum_avx2(buf, len, init));
 +	intptr_t align = ((intptr_t)buf + 0x1f) & ~(intptr_t)0x1f;   
 
 Wonder if its worth adding an ALIGN_UP macro. 
Actually, we have it, it's called ROUND_UP (see util.h). This could be:

	intptr_t align = ROUND_UP(buf, 0x20);

...and maybe we could use sizeof(__m256i) or similar instead of 0x20.

...
  
  +	unsigned int pad = align - (intptr_t)buf;
 +
 +	if (len < pad)
 +		pad = len;
 +
 +	if (pad)
 +		init += sum_16b(buf, pad);
 +
 +	if (len > pad)
 +		init = csum_avx2((void *)align, len - pad, init);
 +
 +	return (uint16_t)~csum_fold(init);
  }
  
  #else /* __AVX2__ */   
  
-- 
Stefano