avoid char signedness trap

diff --git a/ext/lmdb-safe/lmdb-safe.cc b/ext/lmdb-safe/lmdb-safe.cc
index 083d0661b317a8b0a841c71e487c0b4f748836dc..4a146feba4e8838395eecf445381e3e1227413bb 100644 (file)
--- a/ext/lmdb-safe/lmdb-safe.cc
+++ b/ext/lmdb-safe/lmdb-safe.cc
@@ -42,7 +42,8 @@ namespace LMDBLS {
 
     size_t headersize = LS_MIN_HEADER_SIZE;
 
-    uint16_t numextra = (val[LS_NUMEXTRA_OFFSET] << 8) + val[LS_NUMEXTRA_OFFSET+1];
+    unsigned char* tmp = (unsigned char*)val.data();
+    uint16_t numextra = (tmp[LS_NUMEXTRA_OFFSET] << 8) + tmp[LS_NUMEXTRA_OFFSET+1];
 
     headersize += numextra * LS_BLOCK_SIZE;