new

1 files changed, 39 insertions, 0 deletions

diff --git a/src/libndb/ndbsubstitute.c b/src/libndb/ndbsubstitute.c
new file mode 100644
index 00000000..46f63712
--- /dev/null
+++ b/src/libndb/ndbsubstitute.c
@@ -0,0 +1,39 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <ndb.h>
+
+/* replace a in t with b, the line structure in b is lost, c'est la vie */
+Ndbtuple*
+ndbsubstitute(Ndbtuple *t, Ndbtuple *a, Ndbtuple *b)
+{
+	Ndbtuple *nt;
+
+	if(a == b)
+		return t;
+	if(b == nil)
+		return ndbdiscard(t, a);
+
+	/* all pointers to a become pointers to b */
+	for(nt = t; nt != nil; nt = nt->entry){
+		if(nt->line == a)
+			nt->line = b;
+		if(nt->entry == a)
+			nt->entry = b;
+	}
+
+	/* end of b chain points to a's successors */
+	for(nt = b; nt->entry; nt = nt->entry){
+		nt->line = nt->entry;
+	}
+	nt->line = a->line;
+	nt->entry = a->entry;
+
+	a->entry = nil;
+	ndbfree(a);
+
+	if(a == t)
+		return b;
+	else
+		return t;
+}