[m-rev.] for review: add a reverse_bytes/1 function for the 16- and 32-bit types

[Peter Wang]

On Thu, 21 Sep 2017 21:06:26 -0400 (EDT), Julien Fischer <jfischer at opturion.com> wrote:
> 
> Add a reverse_bytes/1 function for the 16- and 32-bit types.
> 
> Add functions for reversing the bytes in the int16, int32, uint16 and uint32
> types.  These are intended for use in implementing endianness conversions.
> 
> library/int16.m:
> library/uint16.m:
> library/int32.m:
> library/uint32.m:
>      As above.
> 
> Julien.
> 
> diff --git a/library/int16.m b/library/int16.m
> index 359bbe9..651681d 100644
> --- a/library/int16.m
> +++ b/library/int16.m
...
> @@ -388,6 +394,37 @@ max_int16 = 32_767_i16.
> 
>   %---------------------------------------------------------------------------%
> 
> +:- pragma foreign_proc("C",
> +    reverse_bytes(A::in) = (B::out),
> +    [will_not_call_mercury, promise_pure, thread_safe],
> +"
> +#if defined(MR_GNUC) || defined(MR_CLANG)
> +    B = (int16_t) __builtin_bswap16((uint16_t)A);
> +#else
> +    B = ((uint16_t)A >> 8) | (A << 8);
> +#endif
> +").

I find this kind of code easier to follow with the masks indicating the
bits that will be kept, as in the int32 version.

It looks fine, otherwise.

Peter