[Xen-changelog] [xen-unstable] x86, time: Fix scale_reciprocal().

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1228488398 0
# Node ID c520af4bde59d5756d6c58014d5ae0b9011840bc
# Parent  4ffd935c08a3e88fa67328efc4f7bbdbce4a162b
x86, time: Fix scale_reciprocal().
Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>
---
 xen/arch/x86/time.c |   19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

diff -r 4ffd935c08a3 -r c520af4bde59 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       Fri Dec 05 13:06:57 2008 +0000
+++ b/xen/arch/x86/time.c       Fri Dec 05 14:46:38 2008 +0000
@@ -152,14 +152,23 @@ static inline u64 scale_delta(u64 delta,
 /* Compute the reciprocal of the given time_scale. */
 static inline struct time_scale scale_reciprocal(struct time_scale scale)
 {
-    u32 q, r;
+    struct time_scale reciprocal;
+    u32 dividend;
+
+    dividend = 0x80000000u;
+    reciprocal.shift = 1 - scale.shift;
+    while ( unlikely(dividend >= scale.mul_frac) )
+    {
+        dividend >>= 1;
+        reciprocal.shift++;
+    }
 
     asm (
         "divl %4"
-        : "=a" (q), "=d" (r)
-        : "0" (1), "1" (0), "r" (scale.mul_frac) );
-
-    return (struct time_scale) { .shift = -scale.shift, .mul_frac = q };
+        : "=a" (reciprocal.mul_frac), "=d" (dividend)
+        : "0" (0), "1" (dividend), "r" (scale.mul_frac) );
+
+    return reciprocal;
 }
 
 /*

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