Move estimate_bisect_steps to libgit.a

This function is used by bisect.c, part of libgit.a while
estimate_bisect_steps stays in builtin/rev-list.c. Move it to bisect.a
so we won't have undefine reference if a standalone program that uses
libgit.a happens to pull it in.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>

bisect.c

@@ -956,3 +956,41 @@ int bisect_next_all(const char *prefix, int no_checkout)
 	return bisect_checkout(bisect_rev_hex, no_checkout);
 }
 
+static inline int log2i(int n)
+{
+	int log2 = 0;
+
+	for (; n > 1; n >>= 1)
+		log2++;
+
+	return log2;
+}
+
+static inline int exp2i(int n)
+{
+	return 1 << n;
+}
+
+/*
+ * Estimate the number of bisect steps left (after the current step)
+ *
+ * For any x between 0 included and 2^n excluded, the probability for
+ * n - 1 steps left looks like:
+ *
+ * P(2^n + x) == (2^n - x) / (2^n + x)
+ *
+ * and P(2^n + x) < 0.5 means 2^n < 3x
+ */
+int estimate_bisect_steps(int all)
+{
+	int n, x, e;
+
+	if (all < 3)
+		return 0;
+
+	n = log2i(all);
+	e = exp2i(n);
+	x = all - e;
+
+	return (e < 3 * x) ? n : n - 1;
+}

builtin/rev-list.c

@@ -201,45 +201,6 @@ static void show_edge(struct commit *commit)
 	printf("-%s\n", sha1_to_hex(commit->object.sha1));
 }
 
-static inline int log2i(int n)
-{
-	int log2 = 0;
-
-	for (; n > 1; n >>= 1)
-		log2++;
-
-	return log2;
-}
-
-static inline int exp2i(int n)
-{
-	return 1 << n;
-}
-
-/*
- * Estimate the number of bisect steps left (after the current step)
- *
- * For any x between 0 included and 2^n excluded, the probability for
- * n - 1 steps left looks like:
- *
- * P(2^n + x) == (2^n - x) / (2^n + x)
- *
- * and P(2^n + x) < 0.5 means 2^n < 3x
- */
-int estimate_bisect_steps(int all)
-{
-	int n, x, e;
-
-	if (all < 3)
-		return 0;
-
-	n = log2i(all);
-	e = exp2i(n);
-	x = all - e;
-
-	return (e < 3 * x) ? n : n - 1;
-}
-
 void print_commit_list(struct commit_list *list,
 		       const char *format_cur,
 		       const char *format_last)