Merge tag 'ceph-for-4.9-rc1' of git://github.com/ceph/ceph-client

[cascardo/linux.git] / net / ceph / crush / mapper.c

diff --git a/net/ceph/crush/mapper.c b/net/ceph/crush/mapper.c
index 5fcfb98..a421e90 100644 (file)
--- a/net/ceph/crush/mapper.c
+++ b/net/ceph/crush/mapper.c
@@ -245,7 +245,7 @@ static int bucket_straw_choose(struct crush_bucket_straw *bucket,
 /* compute 2^44*log2(input+1) */
 static __u64 crush_ln(unsigned int xin)
 {
-       unsigned int x = xin, x1;
+       unsigned int x = xin;
        int iexpon, index1, index2;
        __u64 RH, LH, LL, xl64, result;
 
@@ -253,9 +253,15 @@ static __u64 crush_ln(unsigned int xin)
 
        /* normalize input */
        iexpon = 15;
-       while (!(x & 0x18000)) {
-               x <<= 1;
-               iexpon--;
+
+       /*
+        * figure out number of bits we need to shift and
+        * do it in one step instead of iteratively
+        */
+       if (!(x & 0x18000)) {
+               int bits = __builtin_clz(x & 0x1FFFF) - 16;
+               x <<= bits;
+               iexpon = 15 - bits;
        }
 
        index1 = (x >> 8) << 1;
@@ -267,12 +273,11 @@ static __u64 crush_ln(unsigned int xin)
        /* RH*x ~ 2^48 * (2^15 + xf), xf<2^8 */
        xl64 = (__s64)x * RH;
        xl64 >>= 48;
-       x1 = xl64;
 
        result = iexpon;
        result <<= (12 + 32);
 
-       index2 = x1 & 0xff;
+       index2 = xl64 & 0xff;
        /* LL ~ 2^48*log2(1.0+index2/2^15) */
        LL = __LL_tbl[index2];