[merged mm-nonmm-stable] mul_u64_u64_div_u64-increase-precision-by-conditionally-swapping-a-and-b.patch removed from -mm tree

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The quilt patch titled
     Subject: mul_u64_u64_div_u64: increase precision by conditionally swapping a and b
has been removed from the -mm tree.  Its filename was
     mul_u64_u64_div_u64-increase-precision-by-conditionally-swapping-a-and-b.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Subject: mul_u64_u64_div_u64: increase precision by conditionally swapping a and b
Date: Sun, 3 Mar 2024 10:24:09 +0100

As indicated in the added comment, the algorithm works better if b is big.
As multiplication is commutative, a and b can be swapped.  Do this if a
is bigger than b.

Link: https://lkml.kernel.org/r/20240303092408.662449-2-u.kleine-koenig@xxxxxxxxxxxxxx
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Tested-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 lib/math/div64.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/lib/math/div64.c~mul_u64_u64_div_u64-increase-precision-by-conditionally-swapping-a-and-b
+++ a/lib/math/div64.c
@@ -22,6 +22,7 @@
 #include <linux/export.h>
 #include <linux/math.h>
 #include <linux/math64.h>
+#include <linux/minmax.h>
 #include <linux/log2.h>
 
 /* Not needed on 64bit architectures */
@@ -191,6 +192,20 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u6
 	/* can a * b overflow ? */
 	if (ilog2(a) + ilog2(b) > 62) {
 		/*
+		 * Note that the algorithm after the if block below might lose
+		 * some precision and the result is more exact for b > a. So
+		 * exchange a and b if a is bigger than b.
+		 *
+		 * For example with a = 43980465100800, b = 100000000, c = 1000000000
+		 * the below calculation doesn't modify b at all because div == 0
+		 * and then shift becomes 45 + 26 - 62 = 9 and so the result
+		 * becomes 4398035251080. However with a and b swapped the exact
+		 * result is calculated (i.e. 4398046510080).
+		 */
+		if (a > b)
+			swap(a, b);
+
+		/*
 		 * (b * a) / c is equal to
 		 *
 		 *      (b / c) * a +
_

Patches currently in -mm which might be from u.kleine-koenig@xxxxxxxxxxxxxx are

lib-build_oid_registry-dont-mention-the-full-path-of-the-script-in-output.patch





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