[patch] rint.3: Document that halfway cases are rounded to even.

[patch] rint.3: Document that halfway cases are rounded to even.

[Matt Turner]

Per IEEE-754 rounding rules.

The round(3) page describes the behavior of rint and nearbyint in the
halfway cases by saying:

   These functions round x to the nearest integer, but round halfway
   cases away from zero [...], instead of to the nearest even integer
   like rint(3)

Signed-off-by: Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 man3/rint.3 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/man3/rint.3 b/man3/rint.3
index d1bd302..06724e3 100644
--- a/man3/rint.3
+++ b/man3/rint.3
@@ -92,7 +92,7 @@ and
 functions round their argument to an integer value in floating-point
 format, using the current rounding direction (see
 .BR fesetround (3))
-and without raising the
+and round halfway cases to the nearest even integer, without raising the
 .I inexact
 exception.
 .LP
-- 
2.0.5

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Re: [patch] rint.3: Document that halfway cases are rounded to even.

[Matt Turner]

On Thu, Mar 12, 2015 at 5:43 PM, Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Per IEEE-754 rounding rules.
>
> The round(3) page describes the behavior of rint and nearbyint in the
> halfway cases by saying:
>
>    These functions round x to the nearest integer, but round halfway
>    cases away from zero [...], instead of to the nearest even integer
>    like rint(3)
>
> Signed-off-by: Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---

Sorry, this is not precise -- these functions round halfway cases to
nearest even when the rounding mode is set to round-to-nearest. I'll
send a revised patch.

And for what it's worth, as far as I can tell this rounding behavior
(halfway cases round to nearest even) is defined by IEEE-754 and not
the C language spec. I don't know if that's worth mentioning.
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[patch] rint.3: Document that halfway cases are rounded to even.

[Matt Turner]

Per IEEE-754 rounding rules.

The round(3) page describes the behavior of rint and nearbyint in the
halfway cases by saying:

   These functions round x to the nearest integer, but round halfway
   cases away from zero [...], instead of to the nearest even integer
   like rint(3)

Signed-off-by: Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 man3/rint.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man3/rint.3 b/man3/rint.3
index d1bd302..59402a7 100644
--- a/man3/rint.3
+++ b/man3/rint.3
@@ -94,7 +94,9 @@ format, using the current rounding direction (see
 .BR fesetround (3))
 and without raising the
 .I inexact
-exception.
+exception. When the current rounding direction is to nearest, these
+functions round halfway cases to the even integer in accordance with
+IEEE-754.
 .LP
 The
 .BR rint (),
-- 
2.0.5

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Re: [patch] rint.3: Document that halfway cases are rounded to even.

[Michael Kerrisk (man-pages)]

On 03/13/2015 02:43 AM, Matt Turner wrote:
> Per IEEE-754 rounding rules.
> 
> The round(3) page describes the behavior of rint and nearbyint in the
> halfway cases by saying:
> 
>    These functions round x to the nearest integer, but round halfway
>    cases away from zero [...], instead of to the nearest even integer
>    like rint(3)

Thanks, Matt. Applied.

Cheers,

Michael


> Signed-off-by: Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  man3/rint.3 | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/man3/rint.3 b/man3/rint.3
> index d1bd302..59402a7 100644
> --- a/man3/rint.3
> +++ b/man3/rint.3
> @@ -94,7 +94,9 @@ format, using the current rounding direction (see
>  .BR fesetround (3))
>  and without raising the
>  .I inexact
> -exception.
> +exception. When the current rounding direction is to nearest, these
> +functions round halfway cases to the even integer in accordance with
> +IEEE-754.
>  .LP
>  The
>  .BR rint (),
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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