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div64_u64(): improve precision on 32bit platforms

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The current implementation of div64_u64 for 32bit systems returns an
approximately correct result when the divisor exceeds 32bits.  Since doing
64bit division using 32bit hardware is a long since solved problem we just
use one of the existing proven methods.

Additionally, add a div64_s64 function to correctly handle doing signed
64bit division.

Addresses https://bugzilla.redhat.com/show_bug.cgi?id=616105

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ben Woodard <bwoodard@llnl.gov>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Mark Grondona <mgrondona@llnl.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Brian Behlendorf
2010-10-26 14:23:10 -07:00
committed by Linus Torvalds
parent 5d051decfc
commit 658716d19f
3 changed files with 59 additions and 10 deletions
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12
include/linux/math64.h
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@ -35,6 +35,14 @@ static inline u64 div64_u64(u64 dividend, u64 divisor)
return dividend / divisor;
}
/**
* div64_s64 - signed 64bit divide with 64bit divisor
*/
static inline s64 div64_s64(s64 dividend, s64 divisor)
{
return dividend / divisor;
}
#elif BITS_PER_LONG == 32
#ifndef div_u64_rem
@ -53,6 +61,10 @@ extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
extern u64 div64_u64(u64 dividend, u64 divisor);
#endif
#ifndef div64_s64
extern s64 div64_s64(s64 dividend, s64 divisor);
#endif
#endif /* BITS_PER_LONG */
/**