From 94ac2ab3fff96814d7460a27a0e9d004abbd4128 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 19 Jun 2024 23:00:37 +0200 Subject: Merging upstream version 6.9.2. Signed-off-by: Daniel Baumann --- lib/math/div64.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'lib/math/div64.c') diff --git a/lib/math/div64.c b/lib/math/div64.c index 55a81782e2..191761b1b6 100644 --- a/lib/math/div64.c +++ b/lib/math/div64.c @@ -22,6 +22,7 @@ #include #include #include +#include #include /* Not needed on 64bit architectures */ @@ -190,6 +191,20 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) /* 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 * -- cgit v1.2.3