[v2] softfloat: add float128_is_{normal, denormal}

[Qemu-devel] [PATCH v2] softfloat: add float128_is_{normal, denormal}

Posted by David Hildenbrand 5 years, 2 months ago

Needed on s390x, to test for the data class of a number. So it will
gain soon a user.

A number is considered normal if the exponent is neither 0 nor all 1's.
That can be checked by adding 1 to the exponent, and comparing against
>= 2 after dropping an eventual overflow into the sign bit.

While at it, convert the other floatXX_is_normal functions to use a
similar, less error prone calculation, as suggested by Richard H.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/fpu/softfloat.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/fpu/softfloat.h b/include/fpu/softfloat.h
index 38a5e99cf3..3ff5215b81 100644
--- a/include/fpu/softfloat.h
+++ b/include/fpu/softfloat.h
@@ -466,7 +466,7 @@ static inline int float32_is_zero_or_denormal(float32 a)
 
 static inline bool float32_is_normal(float32 a)
 {
-    return ((float32_val(a) + 0x00800000) & 0x7fffffff) >= 0x01000000;
+    return (((float32_val(a) >> 23) + 1) & 0xff) >= 2;
 }
 
 static inline bool float32_is_denormal(float32 a)
@@ -622,7 +622,7 @@ static inline int float64_is_zero_or_denormal(float64 a)
 
 static inline bool float64_is_normal(float64 a)
 {
-    return ((float64_val(a) + (1ULL << 52)) & -1ULL >> 1) >= 1ULL << 53;
+    return (((float64_val(a) >> 52) + 1) & 0x7ff) >= 2;
 }
 
 static inline bool float64_is_denormal(float64 a)
@@ -940,6 +940,16 @@ static inline int float128_is_zero_or_denormal(float128 a)
     return (a.high & 0x7fff000000000000LL) == 0;
 }
 
+static inline bool float128_is_normal(float128 a)
+{
+    return (((a.high >> 48) + 1) & 0x7fff) >= 2;
+}
+
+static inline bool float128_is_denormal(float128 a)
+{
+    return float128_is_zero_or_denormal(a) && !float128_is_zero(a);
+}
+
 static inline int float128_is_any_nan(float128 a)
 {
     return ((a.high >> 48) & 0x7fff) == 0x7fff &&
-- 
2.17.2

Re: [Qemu-devel] [PATCH v2] softfloat: add float128_is_{normal, denormal}

Posted by Richard Henderson 5 years, 2 months ago

On 2/6/19 9:10 AM, David Hildenbrand wrote:
> Needed on s390x, to test for the data class of a number. So it will
> gain soon a user.
> 
> A number is considered normal if the exponent is neither 0 nor all 1's.
> That can be checked by adding 1 to the exponent, and comparing against
>> = 2 after dropping an eventual overflow into the sign bit.
> While at it, convert the other floatXX_is_normal functions to use a
> similar, less error prone calculation, as suggested by Richard H.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  include/fpu/softfloat.h | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)


Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~

Re: [Qemu-devel] [PATCH v2] softfloat: add float128_is_{normal, denormal}

Posted by Alex Bennée 5 years, 2 months ago

David Hildenbrand <david@redhat.com> writes:

> Needed on s390x, to test for the data class of a number. So it will
> gain soon a user.
>
> A number is considered normal if the exponent is neither 0 nor all 1's.
> That can be checked by adding 1 to the exponent, and comparing against
>>= 2 after dropping an eventual overflow into the sign bit.
>
> While at it, convert the other floatXX_is_normal functions to use a
> similar, less error prone calculation, as suggested by Richard H.

Queued to fpu/next, thanks.

--
Alex Bennée