@@ -73,7 +73,7 @@ static inline int ubi_dbg_is_bgt_disabled(const struct ubi_device *ubi)
static inline int ubi_dbg_is_bitflip(const struct ubi_device *ubi)
{
if (ubi->dbg.emulate_bitflips)
- return !(prandom_u32() % 200);
+ return prandom_u32() < 0xffffffff/200;
return 0;
}
@@ -87,7 +87,7 @@ static inline int ubi_dbg_is_bitflip(const struct ubi_device *ubi)
static inline int ubi_dbg_is_write_failure(const struct ubi_device *ubi)
{
if (ubi->dbg.emulate_io_failures)
- return !(prandom_u32() % 500);
+ return prandom_u32() < 0xffffffff/500;
return 0;
}
@@ -101,7 +101,7 @@ static inline int ubi_dbg_is_write_failure(const struct ubi_device *ubi)
static inline int ubi_dbg_is_erase_failure(const struct ubi_device *ubi)
{
if (ubi->dbg.emulate_io_failures)
- return !(prandom_u32() % 400);
+ return prandom_u32() < 0xffffffff/400;
return 0;
}
@@ -2444,9 +2444,10 @@ int dbg_check_nondata_nodes_order(struct ubifs_info *c, struct list_head *head)
return 0;
}
-static inline int chance(unsigned int n, unsigned int out_of)
+static bool chance(unsigned int n, unsigned int out_of)
{
- return !!((prandom_u32() % out_of) + 1 <= n);
+ /* RHS is a constant expression */
+ return prandom_u32() < ((u64)n << 32) / out_of;
}
Not only is "prandom_u32() % d" an inefficient way to obtain a random number, but "prandom_u32_max(d) < n" is an inefficient way to return true with probability n/d. Where n and d are compile-time constants, the efficient way to do this test is "prandom_u32() < ((u64)n << 32)/d. If n == 1 and d is not a power of 2, then 0xffffffff/d == 0x100000000/d works just as well and avoids some 64-bit arithmetic. Signed-off-by: George Spelvin <lkml@sdf.org> Cc: Richard Weinberger <richard@nod.at> Cc: Artem Bityutskiy <dedekind1@gmail.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: linux-mtd@lists.infradead.org --- drivers/mtd/ubi/debug.h | 6 +++--- fs/ubifs/debug.c | 5 +++-- 2 files changed, 6 insertions(+), 5 deletions(-)