diff --git a/checkin_notes b/checkin_notes
index b1e6eaeb71..581f146a52 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -4260,3 +4260,13 @@ Rom    30 Apr 2009
 
 David  1 May 2009
     - removed outdated translation files; updated template
+
+David  1 May 2009
+    - sample bitwise validator: make it work for binary files
+        fixes #886, #887
+
+    lib/
+        md5_file.h
+        util.cpp,h
+    sched/
+        sample_bitwise_validator.cpp
diff --git a/lib/md5_file.h b/lib/md5_file.h
index 891af1971c..a21b8a2c20 100644
--- a/lib/md5_file.h
+++ b/lib/md5_file.h
@@ -28,8 +28,7 @@ extern int md5_block(const unsigned char* data, int nbytes, char* output);
 
 extern std::string md5_string(const unsigned char* data, int nbytes);
 
-inline std::string md5_string(std::string const& data)
-{
+inline std::string md5_string(std::string const& data) {
     return md5_string((const unsigned char*) data.c_str(), (int)data.size());
 }
 
diff --git a/lib/util.cpp b/lib/util.cpp
index 4dd0f89736..8b31bd39e4 100644
--- a/lib/util.cpp
+++ b/lib/util.cpp
@@ -306,8 +306,8 @@ void boinc_crash() {
 
 // read file (at most max_len chars, if nonzero) into malloc'd buf
 //
-int read_file_malloc(const char* path, char*& buf, int max_len, bool tail) {
-    int retval, isize;
+int read_file_malloc(const char* path, char*& buf, size_t max_len, bool tail) {
+    int retval;
     double size;
 
     retval = file_size(path, size);
@@ -328,7 +328,7 @@ int read_file_malloc(const char* path, char*& buf, int max_len, bool tail) {
         size = max_len;
     }
 #endif
-    isize = (int) size;
+    size_t isize = size;
     buf = (char*)malloc(isize+1);
     size_t n = fread(buf, 1, isize, f);
     buf[n] = 0;
@@ -338,7 +338,7 @@ int read_file_malloc(const char* path, char*& buf, int max_len, bool tail) {
 
 // read file (at most max_len chars, if nonzero) into string
 //
-int read_file_string(const char* path, string& result, int max_len, bool tail) {
+int read_file_string(const char* path, string& result, size_t max_len, bool tail) {
     result.erase();
     int retval;
     char* buf;
diff --git a/lib/util.h b/lib/util.h
index 7e47b1f158..2548d85cae 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -70,9 +70,19 @@ extern int boinc_calling_thread_cpu_time(double&);
 //
 extern void mysql_timestamp(double, char*);
 
+// fake a crash
+//
 extern void boinc_crash();
-extern int read_file_malloc(const char* path, char*&, int max_len=0, bool tail=false);
-extern int read_file_string(const char* path, std::string&, int max_len=0, bool tail=false);
+
+// read files into memory.
+// Use only for non-binary files; returns null-terminated string.
+//
+extern int read_file_malloc(
+    const char* path, char*& result, size_t max_len=0, bool tail=false
+);
+extern int read_file_string(
+    const char* path, std::string& result, size_t max_len=0, bool tail=false
+);
 
 #ifdef _WIN32
 
diff --git a/sched/sample_bitwise_validator.cpp b/sched/sample_bitwise_validator.cpp
index 07db987c85..0279e35713 100644
--- a/sched/sample_bitwise_validator.cpp
+++ b/sched/sample_bitwise_validator.cpp
@@ -15,7 +15,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
 
-// A sample validator that grants credit if the majority of results are
+// A sample validator that requires a majority of results to be
 // bitwise identical.
 // This is useful only if either
 // 1) your application does no floating-point math, or
@@ -31,24 +31,15 @@
 using std::string;
 using std::vector;
 
-struct FILE_CKSUM {
-    string md5sum;
-
-    FILE_CKSUM(string& filedata) {
-        md5sum = md5_string(filedata);
-    }
-    ~FILE_CKSUM(){}
-};
-
 struct FILE_CKSUM_LIST {
-    vector<FILE_CKSUM> files;
+    vector<string> files;   // list of MD5s of files
     ~FILE_CKSUM_LIST(){}
 };
 
 bool files_match(FILE_CKSUM_LIST& f1, FILE_CKSUM_LIST& f2) {
     if (f1.files.size() != f2.files.size()) return false;
     for (unsigned int i=0; i<f1.files.size(); i++) {
-        if (f1.files[i].md5sum != f2.files[i].md5sum) return false;
+        if (f1.files[i] != f2.files[i]) return false;
     }
     return true;
 }
@@ -57,6 +48,8 @@ int init_result(RESULT& result, void*& data) {
     int retval;
     FILE_CKSUM_LIST* fcl = new FILE_CKSUM_LIST;
     vector<FILE_INFO> files;
+    char md5_buf[MD5_LEN];
+    double nbytes;
 
     retval = get_output_file_infos(result, files);
     if (retval) {
@@ -67,14 +60,14 @@ int init_result(RESULT& result, void*& data) {
         return retval;
     }
 
-    string filedata;
     for (unsigned int i=0; i<files.size(); i++) {
         FILE_INFO& fi = files[i];
         if (fi.no_validate) continue;
-        retval = read_file_string(fi.path.c_str(), filedata);
+        retval = md5_file(fi.path.c_str(), md5_buf, nbytes);
         if (retval) {
             if (fi.optional) {
-                filedata = "";
+                strcpy(md5_buf, "");
+                    // indicate file is missing; not the same as md5("")
             } else {
                 log_messages.printf(MSG_CRITICAL,
                     "[RESULT#%d %s] Couldn't open %s\n",
@@ -83,8 +76,7 @@ int init_result(RESULT& result, void*& data) {
                 return retval;
             }
         }
-        FILE_CKSUM fc(filedata);
-        fcl->files.push_back(fc);
+        fcl->files.push_back(string(md5_buf));
     }
     data = (void*) fcl;
     return 0;