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Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
math64: New separate div64_u64_rem helper
Commit f792685006274a850e6cc0ea9ade275ccdfc90bc ("math64: New
div64_u64_rem helper") implemented div64_u64 in terms of div64_u64_rem.
But div64_u64_rem was removed because it slowed down div64_u64 (and
there were no other users of div64_u64_rem).
Device Mapper's I/O statistics support has a need for div64_u64_rem;
reintroduce this helper as a separate method that doesn't slow down
div64_u64, especially on 32-bit systems.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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include/linux/math64.h
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include/linux/math64.h
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}
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/**
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* div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
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*/
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static inline u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
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{
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*remainder = dividend % divisor;
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return dividend / divisor;
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}
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/**
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* div64_u64 - unsigned 64bit divide with 64bit divisor
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*/
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static inline u64 div64_u64(u64 dividend, u64 divisor)
···
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#ifndef div_s64_rem
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extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
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#endif
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#ifndef div64_u64_rem
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extern u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder);
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#endif
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#ifndef div64_u64
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lib/div64.c
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lib/div64.c
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#endif
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/**
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* div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
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* @dividend: 64bit dividend
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* @divisor: 64bit divisor
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* @remainder: 64bit remainder
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*
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* This implementation is a comparable to algorithm used by div64_u64.
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* But this operation, which includes math for calculating the remainder,
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* is kept distinct to avoid slowing down the div64_u64 operation on 32bit
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* systems.
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*/
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#ifndef div64_u64_rem
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u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
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{
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u32 high = divisor >> 32;
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u64 quot;
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if (high == 0) {
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u32 rem32;
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quot = div_u64_rem(dividend, divisor, &rem32);
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*remainder = rem32;
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} else {
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int n = 1 + fls(high);
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quot = div_u64(dividend >> n, divisor >> n);
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if (quot != 0)
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quot--;
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*remainder = dividend - quot * divisor;
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if (*remainder >= divisor) {
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quot++;
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*remainder -= divisor;
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}
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}
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return quot;
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}
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EXPORT_SYMBOL(div64_u64_rem);
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#endif
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/**
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* div64_u64 - unsigned 64bit divide with 64bit divisor
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* @dividend: 64bit dividend
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* @divisor: 64bit divisor