fix resume on reverse value index

1 files changed, 21 insertions, 7 deletions

diff --git a/database/src/kv/index.rs b/database/src/kv/index.rs
index dd2471b..5505079 100644
--- a/database/src/kv/index.rs
+++ b/database/src/kv/index.rs
@@ -127,17 +127,21 @@ pub fn iter_index<'a>(
         }
         Sort::Value(value_sort) => {
             assert!(value_sort.offset.is_none(), "TODO");
-            let mut start = prefix.clone();
+            let (mut start, rev) = match value_sort.order {
+                SortOrder::Ascending => (prefix.clone(), false),
+                SortOrder::Descending => (inc_key(prefix.clone()), true),
+            };
             if let Some(resume) = resume {
-                start.extend(resume);
-                start = inc_key(start);
+                start = prefix.iter().copied().chain(resume).collect();
+                if rev {
+                    start = dec_key(start);
+                } else {
+                    start = inc_key(start);
+                }
             }
             Box::new(
                 PrefixIterator {
-                    inner: match value_sort.order {
-                        SortOrder::Ascending => txn.iter(&start, false)?,
-                        SortOrder::Descending => txn.iter(&inc_key(prefix.clone()), true)?,
-                    },
+                    inner: txn.iter(&start, rev)?,
                     prefix: prefix.clone().into(),
                 }
                 .map(move |k| {
@@ -164,6 +168,16 @@ fn inc_key(mut k: Vec<u8>) -> Vec<u8> {
     }
     k
 }
+fn dec_key(mut k: Vec<u8>) -> Vec<u8> {
+    for v in k.iter_mut().rev() {
+        let (nv, carry) = v.overflowing_sub(1);
+        *v = nv;
+        if !carry {
+            break;
+        }
+    }
+    k
+}
 
 fn randomize(mut x: u64) -> u64 {
     for _ in 0..15 {