linux-kernel - [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 24 Oct 2023 18:18:15 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        David Laight <David.Laight@...LAB.COM>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Vasily Gorbik <gor@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        kernel@...labora.com
Subject: [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO_OVERFLOW

Add a new DIV_ROUND_UP helper, which cannot overflow when
big numbers are being used.

Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
---
 include/linux/math.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/math.h b/include/linux/math.h
index dd4152711de7..f80bfb375ab9 100644
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -36,6 +36,17 @@
 
 #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP
 
+/**
+ * DIV_ROUND_UP_NO_OVERFLOW - divide two numbers and always round up
+ * @n: numerator / dividend
+ * @d: denominator / divisor
+ *
+ * This functions does the same as DIV_ROUND_UP, but internally uses a
+ * division and a modulo operation instead of math tricks. This way it
+ * avoids overflowing when handling big numbers.
+ */
+#define DIV_ROUND_UP_NO_OVERFLOW(n, d) (((n) / (d)) + !!((n) % (d)))
+
 #define DIV_ROUND_DOWN_ULL(ll, d) \
 	({ unsigned long long _tmp = (ll); do_div(_tmp, d); _tmp; })
 
-- 
2.42.0