Re: [PATCH 2/8] softfloat: Use int128.h for some operations

[David Hildenbrand]

On 24.09.20 03:24, Richard Henderson wrote:
> Use our Int128, which wraps the compiler's __int128_t,
> instead of open-coding left shifts and arithmetic.
> We'd need to extend Int128 to have unsigned operations
> to replace more than these three.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  include/fpu/softfloat-macros.h | 39 +++++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/include/fpu/softfloat-macros.h b/include/fpu/softfloat-macros.h
> index 57845f8af0..95d88d05b8 100644
> --- a/include/fpu/softfloat-macros.h
> +++ b/include/fpu/softfloat-macros.h
> @@ -84,6 +84,7 @@ this code that are retained.
>  
>  #include "fpu/softfloat-types.h"
>  #include "qemu/host-utils.h"
> +#include "qemu/int128.h"
>  
>  
> /*----------------------------------------------------------------------------
>  | Shifts `a' right by the number of bits given in `count'.  If any nonzero
> @@ -352,13 +353,11 @@ static inline void shortShift128Left(uint64_t a0, 
> uint64_t a1, int count,
>  static inline void shift128Left(uint64_t a0, uint64_t a1, int count,
>                                  uint64_t *z0Ptr, uint64_t *z1Ptr)
>  {
> -    if (count < 64) {
> -        *z1Ptr = a1 << count;
> -        *z0Ptr = count == 0 ? a0 : (a0 << count) | (a1 >> (-count & 63));
> -    } else {
> -        *z1Ptr = 0;
> -        *z0Ptr = a1 << (count - 64);
> -    }
> +    Int128 a = int128_make128(a1, a0);
> +    Int128 z = int128_lshift(a, count);
> +
> +    *z0Ptr = int128_gethi(z);
> +    *z1Ptr = int128_getlo(z);
>  }
>  
>  
> /*----------------------------------------------------------------------------
> @@ -405,15 +404,15 @@ static inline void
>  
> *----------------------------------------------------------------------------*/
>  
>  static inline void
> - add128(
> -     uint64_t a0, uint64_t a1, uint64_t b0, uint64_t b1, uint64_t *z0Ptr, 
> uint64_t *z1Ptr )
> +add128(uint64_t a0, uint64_t a1, uint64_t b0, uint64_t b1,
> +       uint64_t *z0Ptr, uint64_t *z1Ptr)
>  {
> -    uint64_t z1;
> -
> -    z1 = a1 + b1;
> -    *z1Ptr = z1;
> -    *z0Ptr = a0 + b0 + ( z1 < a1 );
> +    Int128 a = int128_make128(a1, a0);
> +    Int128 b = int128_make128(b1, b0);
> +    Int128 z = int128_add(a, b);
>  
> +    *z0Ptr = int128_gethi(z);
> +    *z1Ptr = int128_getlo(z);
>  }
>  
>  
> /*----------------------------------------------------------------------------
> @@ -463,13 +462,15 @@ static inline void
>  
> *----------------------------------------------------------------------------*/
>  
>  static inline void
> - sub128(
> -     uint64_t a0, uint64_t a1, uint64_t b0, uint64_t b1, uint64_t *z0Ptr, 
> uint64_t *z1Ptr )
> +sub128(uint64_t a0, uint64_t a1, uint64_t b0, uint64_t b1,
> +       uint64_t *z0Ptr, uint64_t *z1Ptr)
>  {
> +    Int128 a = int128_make128(a1, a0);
> +    Int128 b = int128_make128(b1, b0);
> +    Int128 z = int128_sub(a, b);
>  
> -    *z1Ptr = a1 - b1;
> -    *z0Ptr = a0 - b0 - ( a1 < b1 );
> -
> +    *z0Ptr = int128_gethi(z);
> +    *z1Ptr = int128_getlo(z);
>  }
>  
>  
> /*----------------------------------------------------------------------------
> 

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

-- 
Thanks,

David / dhildenb