gcs: fix pseudo-code for filter construction, N is size of items, not…

… block

gcs_light_client.mediawiki

@@ -527,31 +527,36 @@ Given a Bitcoin block, a full-node constructs a <code>Normal</code> compact
 filter as follows:
 <pre>
 construct_normal_gcs_filter(block, fp) -> []byte:
-
     let siphash_key = block.hash()[:16]
 
     let P = 1 << fp
-    let N = len(block.transactions)
-    let F = N * P
 
-    items = []
+    let raw_items = []
     for tx in block.transactions:
         if tx.is_coinbase():
-           continue
+            continue
 
         for input in tx.inputs:
-            input_bytes = input.hash || input.index
-            let item = siphash(siphash_key, input_bytes) % F
-            items.append(item)
+            // Inputs serialized as they are on the wire in transactions.
+            // Input index serialized in little-endian.
+            let input_bytes = input.hash || input.index
+            raw_items.append(input_bytes)
 
         for output in tx.outputs:
-            output_bytes = extract_push_datas(output.script)
-            let item = siphash(siphash_key, output_bytes) % F
-            items.append(time)
+            let output_bytes = extract_push_datas(output.script)
+            raw_items.append(output_bytes)
+
+    let N = len(raw_items)
+    let F = N * P
 
-     items.sort()
+    let hashed_items = []
+    for raw_item in raw_items:
+        let hashed_item = siphash_key(siphash_key, raw_item) % F
+        hashed_items.append(hashed_item)
 
-     gcs_compress(items, fp)
+    hashed_items.sort()
+
+    gcs_compress(hashed_items, fp)
 </pre>
 
 
@@ -562,30 +567,34 @@ construct_extended_gcs_filter(block, fp) -> []byte:
     let siphash_key = block.hash()[:16]
 
     let P = 1 << fp
-    let N = len(block.transactions)
-    let M = N * P
 
-    items = []
+    let raw_items = []
     for tx in block.transactions:
-        txid = tx.hash()
-        items.append(txid)
+        let txid = tx.hash()
+        raw_items.append(txid)
 
         if tx.is_coinbase():
            continue
 
         for input in tx.inputs:
             for wit_elem in input.witness:
-                let item = siphash(siphash_key, wit_elem) % M
-                items.append(item)
+                raw_items.append(wit_elem)
 
-            sig_script_pushes = extract_push_datas(input.sig_script)
+            let sig_script_pushes = extract_push_datas(input.sig_script)
             for push in sig_script_pushes:
-                let item = siphash(siphash_key, push) % M
-                items.append(item)
+                raw_items.append(push)
 
-    items.sort()
+    let N = len(raw_items)
+    let F = N * P
+
+    let hashed_items = []
+    for raw_item in raw_items:
+        let hashed_item = siphash_key(siphash_key, raw_item) % F
+        hashed_items.append(hashed_item)
+
+    hashed_items.sort()
 
-    gcs_compress(items, fp)
+    gcs_compress(hashed_items, fp)
 </pre>
 
 ==== Filter Capability Querying ====