Commit eb18cba7 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

math64: New separate div64_u64_rem helper 



Commit f7926850 ("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: default avatarMike 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: default avatarAlasdair G Kergon <agk@redhat.com>
parent f722063e

include/linux/math64.h

+13 −0
Original line number Diff line number Diff line
@@ -30,6 +30,15 @@ static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) 
	return dividend / divisor;

}



/**

 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder

 */

static inline u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)

{

	*remainder = dividend % divisor;

	return dividend / divisor;

}



/**

 * div64_u64 - unsigned 64bit divide with 64bit divisor

 */
@@ -63,6 +72,10 @@ static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder) 
extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);

#endif



#ifndef div64_u64_rem

extern u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder);

#endif



#ifndef div64_u64

extern u64 div64_u64(u64 dividend, u64 divisor);

#endif

lib/div64.c

+40 −0
Original line number Diff line number Diff line
@@ -78,6 +78,46 @@ s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) 
EXPORT_SYMBOL(div_s64_rem);

#endif



/**

 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder

 * @dividend:	64bit dividend

 * @divisor:	64bit divisor

 * @remainder:  64bit remainder

 *

 * This implementation is a comparable to algorithm used by div64_u64.

 * But this operation, which includes math for calculating the remainder,

 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit

 * systems.

 */

#ifndef div64_u64_rem

u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)

{

	u32 high = divisor >> 32;

	u64 quot;



	if (high == 0) {

		u32 rem32;

		quot = div_u64_rem(dividend, divisor, &rem32);

		*remainder = rem32;

	} else {

		int n = 1 + fls(high);

		quot = div_u64(dividend >> n, divisor >> n);



		if (quot != 0)

			quot--;



		*remainder = dividend - quot * divisor;

		if (*remainder >= divisor) {

			quot++;

			*remainder -= divisor;

		}

	}



	return quot;

}

EXPORT_SYMBOL(div64_u64_rem);

#endif



/**

 * div64_u64 - unsigned 64bit divide with 64bit divisor

 * @dividend:	64bit dividend

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