Portable fix for ks_find() fencepost error.

Binary search of an array is a notorious example of a simple algorithm
which is hard to get exactly right.  The variant we're using is nice
because it automatically computes the correct insertion point when a
key doesn't exist, but runs into one of the portability corner cases
of signed integer arithemtic in C.  Rather than leave a landmine
waiting to explode if somebody builds this code on a platform where
(-1 >> 1) != -1, we test for the corner case explictly and accept the
miniscule performance hit (which will be lost in other noise anyway).

1 files changed, 2 insertions, 2 deletions

diff --git a/ks_index.c b/ks_index.c
index c093a0a..f506a32 100644
--- a/ks_index.c
+++ b/ks_index.c
@@ -56,8 +56,8 @@ static int ks_find(const hal_ks_index_t * const ksi,
   int hi = ksi->used;
 
   for (;;) {
-    int m = (lo + hi) >> 1;
-    if (m == lo) {
+    int m = (lo + hi) / 2;
+    if (hi == 0 || m == lo) {
       *where = hi;
       return 0;
     }