From: Alejandro Colomar <alx@kernel.org>
Date: Tue, 12 Mar 2024 17:25:17 +0000 (+0100)
Subject: logb.3: floor(log2(fabs(x))) has rounding errors
X-Git-Tag: man-pages-6.7~39
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a4ea5f76215dcf1d8d017eb65ab12919ccf09f3f;p=thirdparty%2Fman-pages.git

logb.3: floor(log2(fabs(x))) has rounding errors

Link: <https://inbox.sourceware.org/libc-alpha/20240305150131.GD3653@qaa.vinc17.org/T/#m3ceecda630012995339bcc5448fee451cf277a8b>
Reported-by: Vincent Lefevre <vincent@vinc17.net>
Suggested-by: Vincent Lefevre <vincent@vinc17.net>
Cc: Morten Welinder <mwelinder@gmail.com>
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---

diff --git a/man3/logb.3 b/man3/logb.3
index 7a1ad2f4a..6d1cb5be8 100644
--- a/man3/logb.3
+++ b/man3/logb.3
@@ -57,9 +57,10 @@ If
 .B FLT_RADIX
 is 2,
 .BI logb( x )
-is equal to
+is similar to
 .BI floor(log2(fabs( x )))\f[R],\f[]
-except that it is probably faster.
+except that the latter may give an incorrect integer
+due to intermediate rounding.
 .P
 If
 .I x