[PATCH] Cygwin: _endian.h: Add AArch64 implementations for `ntohl` and `ntohs`

[Corinna Vinschen]

Hi Thirumalai,

On Jan  5 12:40, Thirumalai Nagalingam wrote:
> Hello Everyone,
> 
> This patch adds AArch64-specific inline asm implementations of __ntohl()
> and __ntohs() in `winsup/cygwin/include/machine/_endian.h`.
> 
> For AArch64 targets, the patch uses the REV and REV16 instructions
> to perform byte swapping, with explicit zero-extension for 16-bit
> values to ensure correct register semantics.
> 
> Comments and reviews are welcome.
> 
> Thanks & regards
> Thirumalai Nagalingam <thirumalai.nagalingam@multicorewareinc.com<mailto:thirumalai.nagalingam@multicorewareinc.com>>
> 
> In-lined patch:
> 
> diff --git a/winsup/cygwin/include/machine/_endian.h b/winsup/cygwin/include/machine/_endian.h
> index dbd4429b8..129cba66b 100644
> --- a/winsup/cygwin/include/machine/_endian.h
> +++ b/winsup/cygwin/include/machine/_endian.h
> @@ -26,16 +26,26 @@ _ELIDABLE_INLINE __uint16_t __ntohs(__uint16_t);
>  _ELIDABLE_INLINE __uint32_t
>  __ntohl(__uint32_t _x)
>  {
> +#if defined(__x86_64__)
>         __asm__("bswap %0" : "=r" (_x) : "0" (_x));
> +#elif defined(__aarch64__)
> +       __asm__("rev %w0, %w0" : "=r" (_x) : "0" (_x));
> +#endif
>         return _x;
>  }
> 
>  _ELIDABLE_INLINE __uint16_t
>  __ntohs(__uint16_t _x)
>  {
> +#if defined(__x86_64__)
>         __asm__("xchgb %b0,%h0"         /* swap bytes           */
>                 : "=Q" (_x)
>                 :  "0" (_x));
> +#elif defined(__aarch64__)
> +       __asm__("uxth %w0, %w0\n\t"
> +               "rev16 %w0, %w0"
> +               : "+r" (_x));
> +#endif
>         return _x;
>  }
 
This looks pretty obvious to me, pushed.


Thanks,
Corinna