[improvement]: more precise CheckMem function

src/hnsw/utils.c

@@ -78,8 +78,13 @@ void CheckMem(int limit, Relation index, usearch_index_t uidx, uint32 n_nodes, c
         double          M = ldb_HnswGetM(index);
         double          mL = 1 / log(M);
         metadata_t      meta = usearch_index_metadata(uidx, &error);
-        // todo:: update sizeof(float) to correct vector size once #19 is merged
-        node_size = UsearchNodeBytes(&meta, meta.dimensions * sizeof(float), (int)round(mL + 1));
+        int vector_bytes_num = divide_round_up(meta.dimensions * GetUsearchBitsPerScalar(GetUsearchScalarKindFromIndexMeta(meta)), 8);
+
+        // use the node size at level `(int)rount(mL + 1)` as the average node size,
+        // the sizes of nodes in different levels is actually not linearly related, but 
+        // since nodes are exponentially distributed between levels, dominated by bottom level,
+        // this is a reasonably good approximation.
+        node_size = UsearchNodeBytes(&meta, vector_bytes_num, (int)round(mL + 1));
     }
     // todo:: there's figure out a way to check this in pg <= 12
 #if PG_VERSION_NUM >= 130000

src/hnsw/utils.h

@@ -17,6 +17,25 @@ uint32                EstimateRowCount(Relation heap);
 int32                 GetColumnAttributeNumber(Relation rel, const char *columnName);
 usearch_metric_kind_t GetMetricKindFromStr(char *metric_kind_str);
 
+inline size_t divide_round_up(size_t num, size_t denominator) {
+    return (num + denominator - 1) / denominator;
+}
+
+inline size_t GetUsearchBitsPerScalar(usearch_scalar_kind_t scalar_kind) {
+    switch (scalar_kind) {
+    case usearch_scalar_f64_k: return 64;
+    case usearch_scalar_f32_k: return 32;
+    case usearch_scalar_f16_k: return 16;
+    case usearch_scalar_i8_k: return 8;
+    case usearch_scalar_b1_k: return 1;
+    default: return 0;
+    }
+}
+
+inline usearch_scalar_kind_t GetUsearchScalarKindFromIndexMeta(metadata_t meta) {
+    return meta.init_options.quantization;
+}
+
 // hoping to throw the error via an assertion, if those are on, before elog(ERROR)-ing as a last resort
 // We prefer Assert() because this function is used in contexts where the stack contains non-POD types
 // in which case elog-s long jumps cause undefined behaviour.