1 files changed, 20 insertions, 2 deletions

diff --git a/src/solvers/coord/dr.h b/src/solvers/coord/dr.h
index 314d4f1..3bc4c6d 100644
--- a/src/solvers/coord/dr.h
+++ b/src/solvers/coord/dr.h
@@ -1,5 +1,5 @@
-#define DREOESEP_CLASSES   UINT64_C(64430)
-#define DREOESEP_MAX       (POW_2_11 * COMB_12_4)
+#define DREOESEP_CLASSES UINT64_C(64430)
+#define DREOESEP_MAX     (POW_2_11 * COMB_12_4)
 
 STATIC uint64_t coord_dreoesep_nosym(cube_t);
 STATIC cube_t invcoord_dreoesep_nosym(uint64_t);
@@ -10,6 +10,8 @@ STATIC cube_t coordinate_dr_cube(uint64_t, const void *);
 STATIC bool coordinate_dr_isnasty(uint64_t, const void *);
 STATIC size_t coordinate_dr_gendata(void *);
 
+STATIC bool is_eoco_solvable(cube_t);
+
 /* TODO: remove the following two when all coordinates are converted to unsigned */
 STATIC uint64_t coord_co_u(cube_t c) { return (uint64_t)coord_co(c); }
 STATIC cube_t invcoord_co_u(uint64_t i) { return invcoord_co((int64_t)i); }
@@ -29,6 +31,7 @@ STATIC coord_t coordinate_dr = {
                 [AXIS_FB] = TRANS_FDr,
         },
         .is_admissible = &solution_lastqt_cw,
+        .is_solvable = &is_eoco_solvable,
         .sym = {
                 .classes = DREOESEP_CLASSES,
                 .max = DREOESEP_MAX,
@@ -100,3 +103,18 @@ coordinate_dr_gendata(void *data)
 {
         return coord_gendata_generic(&coordinate_dr, data);
 }
+
+STATIC bool
+is_eoco_solvable(cube_t cube) {
+        uint8_t c[8], e[12], i, cocount, eocount;
+
+        pieces(&cube, c, e);
+
+        for (i = 0, cocount = 0; i < 8; i++)
+                cocount += (c[i] & COBITS_2) >> COSHIFT;
+
+        for (i = 0, eocount = 0; i < 12; i++)
+                eocount += (e[i] & EOBIT) >> EOSHIFT;
+
+        return cocount % 3 == 0 && eocount % 2 == 0;
+}