Merge pull request #632 from robekras/patch-1

Fix lfs_file_rawseek performance issue

lfs.c

@@ -3100,6 +3100,27 @@ static lfs_soff_t lfs_file_rawseek(lfs_t *lfs, lfs_file_t *file,
         return npos;
     }
 
+    // if we're only reading and our new offset is still in the file's cache
+    // we can avoid flushing and needing to reread the data
+    if (
+#ifndef LFS_READONLY
+        !(file->flags & LFS_F_WRITING)
+#else
+        true
+#endif
+            ) {
+        int oindex = lfs_ctz_index(lfs, &(lfs_off_t){file->pos});
+        lfs_off_t noff = npos;
+        int nindex = lfs_ctz_index(lfs, &noff);
+        if (oindex == nindex
+                && noff >= file->cache.off
+                && noff < file->cache.off + file->cache.size) {
+            file->pos = npos;
+            file->off = noff;
+            return npos;
+        }
+    }
+
     // write out everything beforehand, may be noop if rdonly
     int err = lfs_file_flush(lfs, file);
     if (err) {