9 files changed, 137 insertions, 4 deletions

diff --git a/doc/solvers.md b/doc/solvers.md
index 12df168..b7fe613 100644
--- a/doc/solvers.md
+++ b/doc/solvers.md
@@ -129,17 +129,31 @@ NISS will not be used.
 * Moveset: {U, U', U2, D, D', D2, R2, L2, F2, B2}.
 * Data size: 54MB.
 
-### Solve corners
+### Solve corners (fixed centers)
 
-Solve the corners of the cube. Note: centers are considered fixed,
+Solve the corners of the cube. The centers are considered fixed,
 this is not the same as solving a 2x2x2 cube.
 
-* Name: `coord_DRFIN_UF`. Other rotations in place of `UF` are allowed,
+* Name: `coord_CORNERS_UF`. Other rotations in place of `UF` are allowed,
   but they are irrelevant to the solver. Provided alias: `corners`.
 * Requisites: none.
 * Moveset: HTM (all 18 basic moves).
 * Data size: 1.2MB.
 
+### Solve corners (ignoring centers)
+
+Solve the corners of the cube relative to each other, ignoring centers.
+This is the same as solving a 2x2x2 cube.
+
+* Name: `coord_CORNERSX_UF`. Other rotations in place of `UF` are allowed,
+  but they are irrelevant to the solver. Provided alias: `cornersx`.
+* Requisites: none.
+* Moveset: {U, U', U2, R, R', R2, F, F', F2}. Note: if the given cube
+  has an orientation different from the standard `UF` orientation, the
+  solution will use a different moves. The solution will always only use
+  at most 3 different types of moves (as in U, R, F).
+* Data size: 1.2MB.
+
 ### Undocumented coordinate solvers
 
 There are some coordinate solvers that have not been listed above. These
diff --git a/src/core/constants.h b/src/core/constants.h
index d8f2471..076a483 100644
--- a/src/core/constants.h
+++ b/src/core/constants.h
@@ -366,6 +366,8 @@
     MM_SINGLE(MOVE_F2) | MM_SINGLE(MOVE_B2))
 #define MM18_DR_NOD      (MM18_DR & ~MM18_FACE(MOVE_D))
 #define MM18_HTR         (MM18_ALLMOVES & ~MM18_NOHALFTURNS)
+#define MM18_URF         (\
+    MM18_FACE(MOVE_U) | MM18_FACE(MOVE_R) | MM18_FACE(MOVE_F))
 
 #define TM_SINGLE(t)   (UINT64_C(1) << (uint64_t)(t))
 #define TM_ALLTRANS    UINT64_C(0xFFFFFFFFFFFF)
diff --git a/src/solvers/coord/coord.h b/src/solvers/coord/coord.h
index 2ef8482..98f4d05 100644
--- a/src/solvers/coord/coord.h
+++ b/src/solvers/coord/coord.h
@@ -9,6 +9,7 @@
 #include "drfin.h"
 #include "htr.h"
 #include "corners.h"
+#include "cornersx.h"
 #include "list.h"
 #include "utils.h"
 #include "gendata.h"
diff --git a/src/solvers/coord/cornersx.h b/src/solvers/coord/cornersx.h
new file mode 100644
index 0000000..788db8d
--- /dev/null
+++ b/src/solvers/coord/cornersx.h
@@ -0,0 +1,76 @@
+STATIC bool is_cornersx_solved(uint64_t, const unsigned char *);
+
+STATIC coord_t coordinate_cornersx = {
+        .name = "CORNERSX",
+        .coord = &coordinate_corners_coord,
+        .cube = &coordinate_corners_cube,
+        .isnasty = &coordinate_corners_isnasty,
+        .gendata = coordinate_corners_gendata,
+        .max = CLASSES_CP_48 * POW_3_7,
+        .trans_mask = TM_ALLTRANS,
+        .moves_mask_gendata = MM18_ALLMOVES,
+        .moves_mask_solve = MM18_URF,
+        .is_admissible = &solution_always_valid,
+        .solution_prune = NULL,
+        .is_solvable = &cube_true,
+        .is_solved = &is_cornersx_solved,
+        .allow_niss = false,
+        .pruning_distribution = {
+                [0] = 5,
+                [1] = 11,
+                [2] = 42,
+                [3] = 240,
+                [4] = 1115,
+                [5] = 5848,
+                [6] = 29088,
+                [7] = 133410,
+                [8] = 508020,
+                [9] = 1100543,
+                [10] = 371364,
+                [11] = 2322,
+        },
+        .pruning_max = 11,
+        .sym = {
+                .classes = CLASSES_CP_48,
+                .max = FACT_8,
+                .coord = &coord_cp,
+                .cube = &invcoord_cp,
+                .max2 = POW_3_7,
+                .coord2 = &coord_co,
+                .cube2 = &invcoord_co,
+                .merge = &coordinate_merge_cpco,
+        },
+};
+
+STATIC bool
+is_cornersx_solved(uint64_t coord, const unsigned char *data)
+{
+        /*
+        TODO we use a bit of an ugly trick to check all rotated versions of
+        the cube. We would like to apply rotations, but our oriented_cube_t
+        type does not allow to do this directly (we would just be changing
+        the orientation field, not the cube itself). So we apply slice moves
+        instead. We should make this less ugly.
+        */
+        static uint8_t mt[] = {
+                [MOVE_x] = MOVE_M, [MOVE_x2] = MOVE_M2, [MOVE_x3] = MOVE_M3,
+                [MOVE_y] = MOVE_E, [MOVE_y2] = MOVE_E2, [MOVE_y3] = MOVE_E3,
+                [MOVE_z] = MOVE_S3, [MOVE_z2] = MOVE_S2, [MOVE_z3] = MOVE_S
+        };
+
+        uint8_t i, j;
+        cube_t cube;
+        oriented_cube_t oc;
+
+        cube = coordinate_corners_cube(coord, data);
+        oc.orientation = ORIENTATION_UF;
+        for (i = ORIENTATION_UF; i <= ORIENTATION_BL; i++) {
+                oc.cube = cube;
+                for (j = 0; orientation_moves[i][j] != UINT8_MAX; j++)
+                        oc = move_extended(oc, mt[orientation_moves[i][j]]);
+                if (coordinate_corners_coord(oc.cube, data) == 0)
+                        return true;
+        }
+
+        return false;
+}
diff --git a/src/solvers/coord/list.h b/src/solvers/coord/list.h
index f2b7368..6856c13 100644
--- a/src/solvers/coord/list.h
+++ b/src/solvers/coord/list.h
@@ -7,6 +7,7 @@ coord_t *all_coordinates[] = {
         &coordinate_cpepe,
         &coordinate_htr,
         &coordinate_corners,
+        &coordinate_cornersx,
         NULL
 };
 
diff --git a/src/solvers/coord/types_macros.h b/src/solvers/coord/types_macros.h
index a9e604c..b75fab8 100644
--- a/src/solvers/coord/types_macros.h
+++ b/src/solvers/coord/types_macros.h
@@ -30,7 +30,7 @@ typedef struct {
         bool (*is_admissible)(const solution_moves_t[static 1]);
         bool (*solution_prune)(const solution_moves_t[static 1]);
         bool (*is_solvable)(cube_t);
-        /* if is_solved is nulle, coord == 0 is used */
+        /* if is_solved is null, coord == 0 is used */
         bool (*is_solved)(uint64_t, const unsigned char *);
         uint64_t pruning_distribution[INFO_DISTRIBUTION_LEN];
         uint8_t pruning_max;
diff --git a/src/solvers/dispatch.h b/src/solvers/dispatch.h
index 8147929..3184a28 100644
--- a/src/solvers/dispatch.h
+++ b/src/solvers/dispatch.h
@@ -66,6 +66,7 @@ const char *solver_aliases[][2] = {
         { "htr-drrl", "coord_HTR_LF" },
         { "htr-drfb", "coord_HTR_BU" },
         { "corners", "coord_CORNERS_UF" },
+        { "cornersx", "coord_CORNERSX_UF" },
         { NULL, NULL }
 };
 
diff --git a/tools/421_solvetest_cornersx/scrambles.h b/tools/421_solvetest_cornersx/scrambles.h
new file mode 100644
index 0000000..0a3b75c
--- /dev/null
+++ b/tools/421_solvetest_cornersx/scrambles.h
@@ -0,0 +1,29 @@
+struct {
+        char *scramble;
+        char *solutions;
+} s[] = {
+[0] = {
+        .scramble = "R2 D' F2 B D L2 U L U2 R' D' F2 B2 U F2 D F2 U' L2 D' F2",
+        .solutions =
+                "U R U2 F' U R2 U R F'\n"
+                "U R U' R F R2 F U' F2\n"
+                "U2 R' U F' U F' U R' U2\n"
+                "U R2 U2 F U R' U' F U' F2\n"
+                "U2 F R' F' R2 F' U' F2 U' R\n"
+                "U2 F2 R F' R' U' R U2 F R'\n"
+                "U2 F2 R' U R2 F R' F' U' R\n"
+                "U' F U2 R2 F2 U' F U F' R\n"
+                "U' F' U2 R2 U' R' U' F U' F2\n"
+                "U' F' U2 R2 F2 U F U F' R\n"
+                "R2 U F2 U' R U' F U' R' F2\n"
+                "F' U F2 U F U' F2 R F' U2\n"
+                "F' R' F R' F R' U' R' U' F2\n"
+},
+/*
+TODO: add more scrambles, use https://or18.github.io/RubiksSolverDemo/2x2x2
+to generate test cases.
+*/
+{
+        .scramble = "", /* End-of-list signal */
+}
+};
diff --git a/tools/421_solvetest_cornersx/solvetest.c b/tools/421_solvetest_cornersx/solvetest.c
new file mode 100644
index 0000000..6f67d74
--- /dev/null
+++ b/tools/421_solvetest_cornersx/solvetest.c
@@ -0,0 +1,9 @@
+#define SOLVER       "cornersx"
+#define NISSFLAG     NISSY_NISSFLAG_NORMAL
+#define MINMOVES     0
+#define MAXMOVES     20
+#define MAXSOLUTIONS 500
+#define OPTIMAL      1
+
+#include "scrambles.h"
+#include "../solvetest.h"