Re: [PATCH 01/72] qemu/host-utils: Use __builtin_bitreverseN

[David Hildenbrand]

On 08.05.21 03:46, Richard Henderson wrote:
> Clang has added some builtins for these operations;
> use them if available.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   include/qemu/host-utils.h | 16 ++++++++++++++++
>   1 file changed, 16 insertions(+)
>
> diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
> index cdca2991d8..f1e52851e0 100644
> --- a/include/qemu/host-utils.h
> +++ b/include/qemu/host-utils.h
> @@ -272,6 +272,9 @@ static inline int ctpop64(uint64_t val)
>    */
>   static inline uint8_t revbit8(uint8_t x)
>   {
> +#if __has_builtin(__builtin_bitreverse8)
> +    return __builtin_bitreverse8(x);
> +#else
>       /* Assign the correct nibble position.  */
>       x = ((x & 0xf0) >> 4)
>         | ((x & 0x0f) << 4);
> @@ -281,6 +284,7 @@ static inline uint8_t revbit8(uint8_t x)
>         | ((x & 0x22) << 1)
>         | ((x & 0x11) << 3);
>       return x;
> +#endif
>   }
>   
>   /**
> @@ -289,6 +293,9 @@ static inline uint8_t revbit8(uint8_t x)
>    */
>   static inline uint16_t revbit16(uint16_t x)
>   {
> +#if __has_builtin(__builtin_bitreverse16)
> +    return __builtin_bitreverse16(x);
> +#else
>       /* Assign the correct byte position.  */
>       x = bswap16(x);
>       /* Assign the correct nibble position.  */
> @@ -300,6 +307,7 @@ static inline uint16_t revbit16(uint16_t x)
>         | ((x & 0x2222) << 1)
>         | ((x & 0x1111) << 3);
>       return x;
> +#endif
>   }
>   
>   /**
> @@ -308,6 +316,9 @@ static inline uint16_t revbit16(uint16_t x)
>    */
>   static inline uint32_t revbit32(uint32_t x)
>   {
> +#if __has_builtin(__builtin_bitreverse32)
> +    return __builtin_bitreverse32(x);
> +#else
>       /* Assign the correct byte position.  */
>       x = bswap32(x);
>       /* Assign the correct nibble position.  */
> @@ -319,6 +330,7 @@ static inline uint32_t revbit32(uint32_t x)
>         | ((x & 0x22222222u) << 1)
>         | ((x & 0x11111111u) << 3);
>       return x;
> +#endif
>   }
>   
>   /**
> @@ -327,6 +339,9 @@ static inline uint32_t revbit32(uint32_t x)
>    */
>   static inline uint64_t revbit64(uint64_t x)
>   {
> +#if __has_builtin(__builtin_bitreverse64)
> +    return __builtin_bitreverse64(x);
> +#else
>       /* Assign the correct byte position.  */
>       x = bswap64(x);
>       /* Assign the correct nibble position.  */
> @@ -338,6 +353,7 @@ static inline uint64_t revbit64(uint64_t x)
>         | ((x & 0x2222222222222222ull) << 1)
>         | ((x & 0x1111111111111111ull) << 3);
>       return x;
> +#endif
>   }
>   
>   /* Host type specific sizes of these routines.  */

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb