[PATCH 6/9] random: simplify accounting logic

[Greg Price <price@MIT.EDU>]

This logic is exactly equivalent to the old logic, but it should
be easier to see what it's doing.

The equivalence depends on one fact from outside this function:
when 'r->limit' is false, 'reserved' is zero.  (Well, two facts;
the other is that 'reserved' is never negative.)

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Price <price@mit.edu>
---
 drivers/char/random.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index fe7ecdd..5dffca8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -988,14 +988,10 @@ retry:
 		ibytes = 0;
 	} else {
 		/* If limited, never pull more than available */
-		if (r->limit && ibytes + reserved >= have_bytes)
-			ibytes = have_bytes - reserved;
-
-		if (have_bytes >= ibytes + reserved)
-			entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
-		else
-			entropy_count = reserved << (ENTROPY_SHIFT + 3);
-
+		if (r->limit)
+			ibytes = min_t(size_t, ibytes, have_bytes - reserved);
+		entropy_count = max_t(int, 0,
+			    entropy_count - (ibytes << (ENTROPY_SHIFT + 3)));
 		if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
 			goto retry;
 
-- 
1.8.3.2