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

PATCH In review Matt Turner 2 participants 4 messages Mar 13, 2015 – Mar 22, 2015 3 messages not in the archive Man-pages: manual pages for Linux -- Sections 2, 3, 4, 5, and 7

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PATCH 1/1 rint.3: Document that halfway cases are rounded to even.

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)

---
 man3/rint.3 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
man3/rint.3 +1 -1
index d1bd302..06724e3 100644
@@ -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
Signature · 6 lines
2.0.5

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#2 lore raw
Quoted 11 lines · 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)

---

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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#4 lore raw

PATCH 1/1 rint.3: Document that halfway cases are rounded to even.

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)

---
 man3/rint.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
man3/rint.3 +3 -1
index d1bd302..59402a7 100644
@@ -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 (),
Signature · 6 lines
2.0.5

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A message that is not in the archive (sent off-list or not yet received): 1426211007-9986-1-git-send-email-mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

#6 lore raw
Quoted 8 lines · 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)

Thanks, Matt. Applied.

Cheers,

Michael

Quoted 21 lines
---
 man3/rint.3 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
man3/rint.3 +3 -1
index d1bd302..59402a7 100644
@@ -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 (),
Signature · 7 lines
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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