RE: [PATCH] Added hardfloat conversion from float32 to float64

[Matus Kysel <mkysel@tachyum.com>]

Hi,

I have send patch v2 with proposed changes, please have a look https://lists.nongnu.org/archive/html/qemu-devel/2019-10/msg04264.html

Matus

-----Original Message-----
From: Richard Henderson <richard.henderson@linaro.org> 
Sent: streda 16. októbra 2019 17:38
To: Matus Kysel <mkysel@tachyum.com>; qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>; Alex Bennée <alex.bennee@linaro.org>; Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [PATCH] Added hardfloat conversion from float32 to float64

On 10/16/19 12:32 AM, Matus Kysel wrote:
> +float64 float32_to_float64(float32 a, float_status *status) {
> +    if (unlikely(!float32_is_normal(a))) {
> +        return soft_float32_to_float64(a, status);
> +    } else if (float32_is_zero(a)) {
> +        return float64_set_sign(float64_zero, float32_is_neg(a));
> +    } else {
> +        double r = *(float *)&a;
> +        return *(float64 *)&r;
> +    }
> +}

This is a good idea, since there are no issues with inexact or rounding when converting in this direction.

Please use union_float{32,64} instead of casting.

Your special case for 0 won't fire, since it is already filtered by !float32_is_normal.

So I think this could be written as

    if (likely(float32_is_normal(a))) {
        union_float32 uf;
        union_float64 ud;

        uf.s = a;
        ud.h = uf.h;
        return ud.s;
    } else if (float32_is_zero(a)) {
        return float64_set_sign(float64_zero, float32_is_neg(a));
    } else {
        return soft_float32_to_float64(a);
    }


r~