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Re: [Qemu-devel] [PATCH v1] softfloat: add float128_is_{normal, denormal
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From: |
Richard Henderson |
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Subject: |
Re: [Qemu-devel] [PATCH v1] softfloat: add float128_is_{normal, denormal} |
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Date: |
Wed, 6 Feb 2019 03:08:43 +0000 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
On 2/5/19 4:22 PM, David Hildenbrand wrote:
> +static inline bool float128_is_normal(float128 a)
> +{
> + return ((a.high + (1ULL << 47)) & -1ULL >> 1) >= 1ULL << 48;
I believe this is off by one: 1 << 48 and >= 1 << 49.
The exponent is at [62:48]. The trick is adding 1, letting Inf+NaN overflow
into the sign, masking out the sign, and checking that the result >= 2 to
eliminate Inf+NaN (0) and Zero+Denormal (1).
I think this is clearer as
(((a.high >> 48) + 1) & 0x7fff) >= 2.
It might be worth applying this to the other formats for clarity...
r~