Re: [Qemu-devel] [PATCH 1/9] softfloat: Introduce float32_to_uint64_round_to_zero

[Peter Maydell]

On 26 March 2014 20:45, Tom Musta <address@hidden> wrote:
> This change adds the float32_to_uint64_round_to_zero function to the softfloat
> library.  This function fills out the complement of float32 to INT 
> round-to-zero
> conversion rountines, where INT is {int32_t, uint32_t, int64_t, uint64_t}.
>
> This contribution can be licensed under either the softfloat-2a or -2b
> license.
>
> Signed-off-by: Tom Musta <address@hidden>
> Tested-by: Tom Musta <address@hidden>
> ---
>  fpu/softfloat.c         |   54 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  include/fpu/softfloat.h |    1 +
>  2 files changed, 55 insertions(+), 0 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 5f02c16..d6df78a 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1628,6 +1628,60 @@ uint64 float32_to_uint64(float32 a STATUS_PARAM)
>
>  
> /*----------------------------------------------------------------------------
>  | Returns the result of converting the single-precision floating-point value
> +| `a' to the 64-bit unsigned integer format.  The conversion is
> +| performed according to the IEC/IEEE Standard for Binary Floating-Point
> +| Arithmetic, except that the conversion is always rounded toward zero.  If
> +| `a' is a NaN, the largest unsigned integer is returned.  Otherwise, if the
> +| conversion overflows, the largest unsigned integer is returned.  If the
> +| 'a' is negative, the result is rounded and zero is returned; values that do
> +| not round to zero will raise the inexact flag.
> +*----------------------------------------------------------------------------*/
> +
> +uint64 float32_to_uint64_round_to_zero(float32 a STATUS_PARAM)
> +{
> +    flag aSign;
> +    int_fast16_t aExp, shiftCount;
> +    uint32_t aSig;
> +    uint64_t aSig64;
> +    uint64_t z;

So, float64_to_uint64_round_to_zero() works by temporarily
fiddling with the rounding mode and then calling
float64_to_uint64(). Is there a reason for doing this
function like this rather than in the same way?

thanks
-- PMM