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include/linux/math.h: fix mult_frac() multiple argument evaluation bug

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mult_frac() evaluates _all_ arguments multiple times in the body.

Clarify comment while I'm at it.

Link: https://lkml.kernel.org/r/f9f9fdbb-ec8e-4f5e-a998-2a58627a1a43@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Alexey Dobriyan 2023-05-20 21:25:19 +03:00 committed by Andrew Morton
parent d7a0fe9ef6
commit 048a988326
1 changed files with 11 additions and 11 deletions
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22
include/linux/math.h
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@ -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)