From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH v2] fix mult_frac() multiple argument evaluation bug
Date: Sat, 20 May 2023 21:25:19 +0300 [thread overview]
Message-ID: <f9f9fdbb-ec8e-4f5e-a998-2a58627a1a43@p183> (raw)
In-Reply-To: <20230519153622.f95f74819ecf467c5291de7d@linux-foundation.org>
mult_frac() evaluates _all_ arguments multiple times in the body.
Clarify comment while I'm at it.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
include/linux/math.h | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
__STRUCT_FRACT(u32)
#undef __STRUCT_FRACT
-/*
- * Multiplies an integer by a fraction, while avoiding unnecessary
- * overflow or loss of precision.
- */
-#define mult_frac(x, numer, denom)( \
-{ \
- typeof(x) quot = (x) / (denom); \
- typeof(x) rem = (x) % (denom); \
- (quot * (numer)) + ((rem * (numer)) / (denom)); \
-} \
-)
+/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
+#define mult_frac(x, n, d) \
+({ \
+ typeof(x) x_ = (x); \
+ typeof(n) n_ = (n); \
+ typeof(d) d_ = (d); \
+ \
+ typeof(x_) q = x_ / d_; \
+ typeof(x_) r = x_ % d_; \
+ q * n_ + r * n_ / d_; \
+})
#define sector_div(a, b) do_div(a, b)
prev parent reply other threads:[~2023-05-20 18:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-19 20:24 [PATCH] " Alexey Dobriyan
2023-05-19 22:36 ` Andrew Morton
2023-05-20 18:24 ` Alexey Dobriyan
2023-05-20 18:25 ` Alexey Dobriyan [this message]
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