Re: [PATCH 2/2] lib/hash: avoid implicit conversion to 64 bit number

[Andre Muezerie <andremue@linux.microsoft.com>]

On Wed, Jan 22, 2025 at 04:12:49PM +0000, Bruce Richardson wrote:
> On Wed, Nov 27, 2024 at 05:53:57PM -0800, Andre Muezerie wrote:
> > MSVC issues the warnings below:
> > 
> > 1) ../lib/hash/rte_thash_gf2_poly_math.c(128): warning C4334: '<<':
> >     result of 32-bit shift implicitly converted to 64 bits
> >     (was 64-bit shift intended?)
> > 
> > The code would be better off by using 64 bit numbers to begin with.
> > That eliminates the need for a conversion to 64 bits later.
> > 
> > 2) ../lib/hash/rte_thash.c(568): warning C4334: '<<':
> >     result of 32-bit shift implicitly converted to 64 bits
> >     (was 64-bit shift intended?)
> > 
> > 1ULL should be used as the result of the bit shift gets multiplied
> > by sizeof(uint32_t).
> > 
> > Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> > ---
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> >  lib/hash/rte_thash.c               | 2 +-
> >  lib/hash/rte_thash_gf2_poly_math.c | 6 +++---
> >  2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/hash/rte_thash.c b/lib/hash/rte_thash.c
> > index fa78787143..f076311b57 100644
> > --- a/lib/hash/rte_thash.c
> > +++ b/lib/hash/rte_thash.c
> > @@ -565,7 +565,7 @@ rte_thash_add_helper(struct rte_thash_ctx *ctx, const char *name, uint32_t len,
> >  		offset;
> >  
> >  	ent = rte_zmalloc(NULL, sizeof(struct rte_thash_subtuple_helper) +
> > -		sizeof(uint32_t) * (1 << ctx->reta_sz_log),
> > +		sizeof(uint32_t) * (1ULL << ctx->reta_sz_log),
> >  		RTE_CACHE_LINE_SIZE);
> 
> Is there a reason not to use RTE_BIT64 here too?

Here we are calculating the size to be passed to the second argument of rte_zmalloc, which is of type size_t. size_t is implementation dependent, typically 4 bytes on 32-bit systems and 8 bytes on 64-bit systems, so using 1ULL seems more appropriate.