AP_Filesystem: add crc 32 method

libraries/AP_Filesystem/AP_Filesystem.cpp

@@ -18,6 +18,7 @@
 #include "AP_Filesystem_config.h"
 #include <AP_HAL/HAL.h>
 #include <AP_HAL/Util.h>
+#include <AP_Math/AP_Math.h>
 
 static AP_Filesystem fs;
 
@@ -286,6 +287,37 @@ bool AP_Filesystem::fgets(char *buf, uint8_t buflen, int fd)
     return true;
 }
 
+// run crc32 over file with given name, returns true if successful
+bool AP_Filesystem::crc32(const char *fname, uint32_t& checksum)
+{
+    // Open file in readonly mode
+    int fd = open(fname, O_RDONLY);
+    if (fd == -1) {
+        return false;
+    }
+
+    // Buffer to store data temporarily
+    const ssize_t buff_len = 64;
+    uint8_t buf[buff_len];
+
+    // Read into buffer and run crc
+    ssize_t read_size;
+    do {
+        read_size = read(fd, buf, buff_len);
+        if (read_size == -1) {
+            // Read error, note that we have changed the checksum value in this case
+            close(fd);
+            return false;
+        }
+        checksum = crc_crc32(checksum, buf, MIN(read_size, buff_len));
+    } while (read_size > 0);
+
+    close(fd);
+
+    return true;
+}
+
+
 #if AP_FILESYSTEM_FORMAT_ENABLED
 // format filesystem
 bool AP_Filesystem::format(void)