From: Harlan Stenn <stenn@ntp.org>
Date: Mon, 17 Apr 2023 09:19:46 +0000 (-0500)
Subject: Use correct rounding in mstolfp()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9df359d6d7e8c9b63595f9d908124679ada2e2b4;p=thirdparty%2Fntp.git

Use correct rounding in mstolfp()

bk: 643d0f321WzNkRDNEL3OHseXdQR9AA
---

diff --git a/ChangeLog b/ChangeLog
index fc27b2be9..16486f683 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -79,6 +79,7 @@
              Integrated patch from Brian Utterback. <hart@ntp.org>
 * [Bug 2525] Turn on automake subdir-objects across the project. <hart@ntp.org>
 * [Bug 2410] syslog an error message on panic exceeded. <brian.utterback@oracle.com>
+* Use correct rounding in mstolfp(). perlinger/hart
 * M_ADDF should use u_int32.  <hart@ntp.org>
 * Only define tv_fmt_libbuf() if we will use it. <stenn@ntp.org>
 * Use recv_buffer instead of the longer recv_space.X_recv_buffer. hart/stenn
diff --git a/libntp/mstolfp.c b/libntp/mstolfp.c
index c82b7f590..428f71bdb 100644
--- a/libntp/mstolfp.c
+++ b/libntp/mstolfp.c
@@ -61,17 +61,11 @@ mstolfp(
 	lfp->l_uf |= q;
 	r -= q * 1000u;
 
-	/* numerically, rounding should happen *after* the sign correction
-	 * but that would produce different bit patterns from the previous
-	 * implementation. (off-by-one in the fraction. Neglectible, but
-	 * messy to fix in the unit tests. So we stay with the slightly
-	 * suboptimal calculation...)
-	 */
-	/* round */
-	if (r >= 500)
-		L_ADDUF(lfp, 1u);
 	/* fix sign */
 	if (neg)
 		L_NEG(lfp);
+	/* round */
+	if (r >= 500)
+		L_ADDF(lfp, (neg ? -1 : 1));
 	return 1;
 }