From eb18cba78c2b9250663021e17e1e9cc34630e92a Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Tue, 20 Aug 2013 15:05:17 -0400 Subject: 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 Cc: Stanislaw Gruszka Cc: Ingo Molnar Cc: Frederic Weisbecker Cc: Mikulas Patocka Signed-off-by: Alasdair G Kergon --- lib/div64.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) (limited to 'lib') diff --git a/lib/div64.c b/lib/div64.c index a163b6caef73..4382ad77777e 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -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 -- cgit v1.2.2