diff --git a/Makefile b/Makefile
index 6dba1e9..8550f52 100644
--- a/Makefile
+++ b/Makefile
@@ -89,10 +89,10 @@ CFLAGS    := -std=gnu11
 
 ### dev OR release
 # dev
-#CFLAGS    += -O1
+CFLAGS    += -O1
 #CFLAGS    += -g
 # release
-CFLAGS    += -Ofast
+#CFLAGS    += -Ofast
 
 CFLAGS    += -march=native
 CFLAGS    += -flto
@@ -100,7 +100,7 @@ CFLAGS    += -Wall
 CFLAGS    += -Wextra
 CFLAGS    += -Wmissing-declarations
 # for gprof
-#CFLAGS += -pg
+CFLAGS += -pg
 # Next one may be useful for valgrind (when invalid instructions)
 # CFLAGS += -mno-tbm
 
diff --git a/src/fen.c b/src/fen.c
index 8b34afa..741b2ed 100644
--- a/src/fen.c
+++ b/src/fen.c
@@ -75,7 +75,7 @@ static const char *castle_str = "KQkq";
 static int fen_check(pos_t *pos)
 {
     char *colstr[2] = { "white", "black"};
-    int error = 0, warning = 0;
+    int warning = 0;
 
     /* en passant, depends on who plays next */
     if (pos->en_passant != SQUARE_NONE) {
@@ -130,13 +130,7 @@ static int fen_check(pos_t *pos)
             }
         }
     }
-    if (!(error = pos_check(pos, 0))) {
-        /* TODO: Should it really be here ? */
-        pos->checkers = pos_checkers(pos, pos->turn);
-        pos->pinners = pos_king_pinners(pos, pos->turn);
-        pos->blockers = pos_king_blockers(pos, pos->turn, pos->pinners);
-    }
-    return error ? -1: warning;
+    return pos_ok(pos, 0) ? warning: -1;
 }
 
 /**
diff --git a/src/move-gen.c b/src/move-gen.c
index 14f1d23..1c62ffc 100644
--- a/src/move-gen.c
+++ b/src/move-gen.c
@@ -169,7 +169,7 @@ movelist_t *pos_all_legal(const pos_t *pos, movelist_t *movelist, movelist_t *de
  *  - castling, if king passes an enemy-controlled square (not final square).
  * When immediately known, a few move flags are also applied in these cases:
  *  - castling: M_CASTLE_{K,Q}
- *  - pawn capture (excl. en-passant): M_CAPTURE
+ *  - capture (excl. en-passant): M_CAPTURE
  *  - en-passant: M_EN_PASSANT
  *  - pawn double push: M_DPUSH
  *  - promotion: M_PROMOTION
diff --git a/src/position.c b/src/position.c
index 3ffb827..969e1ae 100644
--- a/src/position.c
+++ b/src/position.c
@@ -187,11 +187,30 @@ bitboard_t pos_checkers(const pos_t *pos, const color_t color)
 }
 
 /**
- * pos_king_pinners_blockers() - set position "pinners" and "blockers".
+ * pos_set_checkers_pinners_blockers() - calculate checkers, pinners and blockers.
  * @pos:   &position
  *
- * set position "pinners" on player-to-play king.
+ * Set position checkers, pinners and blockers on player-to-play king.
+ * It should be faster than @pos_checkers + @pos_set_pinners_blockers, as
+ * some calculation will be done once.
+ */
+/*
+ * void pos_set_checkers_pinners_blockers(pos_t *pos)
+ * {
+ *     bitboard_t b_bb = pos->bb[WHITE][BISHOP] | pos->bb[BLACK][BISHOP];
+ *     bitboard_t r_bb = pos->bb[WHITE][ROOK] | pos->bb[BLACK][ROOK];
+ *     bitboard_t q_bb = pos->bb[WHITE][QUEEN] | pos->bb[BLACK][QUEEN];
  *
+ *     /\* find out first piece on every diagonal *\/
+ *
+ * }
+ */
+
+/**
+ * pos_set_pinners_blockers() - set position pinners and blockers.
+ * @pos:   &position
+ *
+ * set position pinners and blockers on player-to-play king.
  */
 void pos_set_pinners_blockers(pos_t *pos)
 {
@@ -253,7 +272,7 @@ bitboard_t pos_king_blockers(const pos_t *pos, const color_t color, const bitboa
 }
 
 /**
- * pos_check() - extensive position consistency check.
+ * pos_ok() - extensive position consistency check.
  * @pos:    &position
  * @strict: if true, call bug_on() on any error.
  *
@@ -278,9 +297,9 @@ bitboard_t pos_king_blockers(const pos_t *pos, const color_t color, const bitboa
  * TODO: add more checks:
  * - kings attacking each other
  *
- * @Return: Number of detected error (only if @strict is false).
+ * @return: (if @strict is false) return true if check is ok, false otherwise.
  */
-int pos_check(const pos_t *pos, const bool strict)
+bool pos_ok(const pos_t *pos, const bool strict)
 {
     int n, count = 0, bbcount = 0, error = 0;
     bitboard_t tmp;
@@ -324,7 +343,7 @@ int pos_check(const pos_t *pos, const bool strict)
     error += warn_on(sq_dist(pos->king[WHITE], pos->king[BLACK]) < 2);
 
     bug_on(strict && error);
-    return error;
+    return error? false: true;
 }
 
 /**
diff --git a/src/position.h b/src/position.h
index 2a41a68..0e76a06 100644
--- a/src/position.h
+++ b/src/position.h
@@ -165,7 +165,7 @@ bitboard_t pos_checkers(const pos_t *pos, const color_t color);
 bitboard_t pos_king_pinners(const pos_t *pos, const color_t color);
 bitboard_t pos_king_blockers(const pos_t *pos, const color_t color, const bitboard_t );
 
-int pos_check(const pos_t *pos, const bool strict);
+bool pos_ok(const pos_t *pos, const bool strict);
 
 void pos_print(const pos_t *pos);
 void pos_print_mask(const pos_t *pos, const bitboard_t mask);