diff options
author | Mike Snitzer <snitzer@redhat.com> | 2013-08-20 15:05:17 -0400 |
---|---|---|
committer | Mike Snitzer <snitzer@redhat.com> | 2013-08-23 09:02:14 -0400 |
commit | eb18cba78c2b9250663021e17e1e9cc34630e92a (patch) | |
tree | e12eaa9ab3e5fddfd27f7697e7f5b0baf00150e5 /lib | |
parent | f722063ee01c0060488e1000006405449451cfa0 (diff) |
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>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/div64.c | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/lib/div64.c b/lib/div64.c index a163b6caef73..4382ad77777e 100644 --- a/lib/div64.c +++ b/lib/div64.c | |||
@@ -79,6 +79,46 @@ EXPORT_SYMBOL(div_s64_rem); | |||
79 | #endif | 79 | #endif |
80 | 80 | ||
81 | /** | 81 | /** |
82 | * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder | ||
83 | * @dividend: 64bit dividend | ||
84 | * @divisor: 64bit divisor | ||
85 | * @remainder: 64bit remainder | ||
86 | * | ||
87 | * This implementation is a comparable to algorithm used by div64_u64. | ||
88 | * But this operation, which includes math for calculating the remainder, | ||
89 | * is kept distinct to avoid slowing down the div64_u64 operation on 32bit | ||
90 | * systems. | ||
91 | */ | ||
92 | #ifndef div64_u64_rem | ||
93 | u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) | ||
94 | { | ||
95 | u32 high = divisor >> 32; | ||
96 | u64 quot; | ||
97 | |||
98 | if (high == 0) { | ||
99 | u32 rem32; | ||
100 | quot = div_u64_rem(dividend, divisor, &rem32); | ||
101 | *remainder = rem32; | ||
102 | } else { | ||
103 | int n = 1 + fls(high); | ||
104 | quot = div_u64(dividend >> n, divisor >> n); | ||
105 | |||
106 | if (quot != 0) | ||
107 | quot--; | ||
108 | |||
109 | *remainder = dividend - quot * divisor; | ||
110 | if (*remainder >= divisor) { | ||
111 | quot++; | ||
112 | *remainder -= divisor; | ||
113 | } | ||
114 | } | ||
115 | |||
116 | return quot; | ||
117 | } | ||
118 | EXPORT_SYMBOL(div64_u64_rem); | ||
119 | #endif | ||
120 | |||
121 | /** | ||
82 | * div64_u64 - unsigned 64bit divide with 64bit divisor | 122 | * div64_u64 - unsigned 64bit divide with 64bit divisor |
83 | * @dividend: 64bit dividend | 123 | * @dividend: 64bit dividend |
84 | * @divisor: 64bit divisor | 124 | * @divisor: 64bit divisor |