Re: [Qemu-devel] [PATCH 0/6] Get rid of confusing softfloat-specific integer types

[Aurelien Jarno]

On 2016-01-12 12:55, Peter Maydell wrote:
> This patchset removes the confusing softfloat-specific integer
> types int8, uint8, int32, uint32, int64 and uint64, replacing
> them with the standard _t types that they were typedef'd as.
> These frequently got accidentally used outside the softfloat
> code as a simple typo for the standard types (as you can see
> from the various files touched in the diffstat).
> 
> Although there is technically a semantic difference (the
> softfloat types are "at least X bits" whereas the standard
> types are "exactly X bits", the distinction is unlikely to
> make much performance difference and "upgrading" the types to
> use int_fast*_t would require careful code analysis to check we
> weren't accidentally  relying on the type width. It also means
> we might potentially have subtle bugs on only some host platforms,
> which is worth avoiding I think.
> 
> (In particular glibc defines int_fast32_t as a 64 bit type
> on 64 bit systems, which is unlikely to be the most sensible
> type to actually use for performance. I was reading a discussion
> about the _fast_ types from the musl irc channel recently:
> https://gist.github.com/andrewrk/ac66b24a0a202d87cea7
> which suggests that they're in practice not very useful.)

Thanks for doing this change. I hope this time we'll reach a consensus.

> This is admittedly a different decision to the one we made in
> the past for int16/uint16 (commits 94a49d86c536af3, 5aea4c589aa).
> I can do a followup patch which converts our int_fast16_t/uint_fast16_t
> usage to int16_t/uint16_t if people would like.
> (I think the difference is partly that the old int16/uint16 types
> really were bigger than 16 bits so we knew the code was not
> accidentally relying on exactly-16-bitness. Also I have a feeling
> that I was one of those suggesting the _fast_ types, but I have
> changed my mind and think I was wrong back then.) 

Yes please it would be nice if we can use standard consistent type
everywhere.

> I have left the 'flag' type alone. This could reasonably be changed
> to 'bool' if we checked all the uses to make sure they weren't
> accidentally relying on it being an integer type. The type name
> is not such that it will be accidentally used outside softfloat,
> so it's less of an irritant.

Indeed.

> thanks
> -- PMM
> 
> Peter Maydell (6):
>   fpu: Replace int64 typedef with int64_t
>   fpu: Replace uint64 typedef with uint64_t
>   fpu: Replace int32 typedef with int32_t
>   fpu: Replace uint32 typedef with uint32_t
>   fpu: Replace int8 typedef with int8_t
>   fpu: Replace uint8 typedef with uint8_t
> 
>  crypto/secret.c            |   2 +-
>  fpu/softfloat-macros.h     |  26 +++---
>  fpu/softfloat-specialize.h |   2 +-
>  fpu/softfloat.c            | 218 
> ++++++++++++++++++++++-----------------------
>  hw/i386/pc.c               |   2 +-
>  hw/ipmi/isa_ipmi_bt.c      |   2 +-
>  hw/ipmi/isa_ipmi_kcs.c     |   2 +-
>  hw/misc/imx25_ccm.c        |   2 +-
>  hw/misc/imx31_ccm.c        |   2 +-
>  hw/net/vmware_utils.h      |   2 +-
>  hw/net/vmxnet3.c           |   2 +-
>  hw/ppc/spapr_events.c      |   4 +-
>  include/fpu/softfloat.h    |  68 ++++++--------
>  include/hw/i386/pc.h       |   2 +-
>  migration/ram.c            |   2 +-
>  target-alpha/fpu_helper.c  |   2 +-
>  target-mips/kvm.c          |   4 +-
>  target-mips/msa_helper.c   |  36 ++++----
>  target-s390x/kvm.c         |   2 +-
>  tests/vhost-user-test.c    |   2 +-
>  20 files changed, 187 insertions(+), 197 deletions(-)

So I am happy to give a:

Reviewed-by: Aurelien Jarno <address@hidden>


Regards,
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net