Added license information!

1 files changed, 34 insertions, 7 deletions

diff --git a/include/actions.c b/include/actions.c
index 5085330..800a2d4 100644
--- a/include/actions.c
+++ b/include/actions.c
@@ -1,3 +1,20 @@
+/*
+	This file is part of ctak.
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful, but
+	WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+	General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with Takwrap.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
 #include "actions.h"
 
 // ===================================================================
@@ -67,6 +84,7 @@ void action_list_init(void) {
 
 action_list_t *action_list_generate(void) {
 	action_list_t *list = malloc(sizeof(struct action_list_s));
+
 	// TODO: trap errno
 	list->length = 0;
 	list->head = NULL;
@@ -129,16 +147,22 @@ action_list_t *action_list_generate(void) {
 					 * For each direction, generate all possible ordered integer
 					 * partitions of 1 ≤ num ≤ count whose number of summands is
 					 * exactly 1 ≤ summands ≤ min(end_stops[dir], num) -- we
-					 * write summands as steps
+					 * write summands as steps.
+					 *
+					 * We exploit the `gaps' bijection here and elsewhere
+					 * between ordered {integer partitions of n with s summands}
+					 * and {binary strings of length n-1 with s-1 set bits}.
 					 */
 					for (enum MOVE_DIRECTION dir=M_UP; dir<=M_RIGHT; dir++) {
 						for (uint8_t num = 1; num <= count; num++) {
 							for (uint8_t steps = 1;
 									 steps <= end_stops[dir] && steps <= num;
 									 steps++) {
-								// TODO: Generalise to board_size!
-								uint8_t gaps = 0x07 >> (board_size-steps-1);
-								// 0b0000[0111] because 4-1=3 and 5-1=4
+								uint8_t gaps =
+									((1<<(board_size - 2)) - 1) >> (board_size-steps-1);
+								// For 5x5 this givess 0b0000[0XXX] where steps-1 of
+								// those X's are 1s (starting with LSB) because 4-1=3
+								// and 5-1=4
 								do  {
 									/*
 									 * We skip the partition if it calls for multiple
@@ -214,9 +238,12 @@ void action_take(const action_t action) {
 			}
 		}
 	} else {
-		 // not interested in whether we crushed, it will work out by
-		 // anyway because we overwrite the top stone type. See (*) later
-		 // for when we do need to know.
+		/*
+		 * See the discussion around line 135 for an explanation of the
+		 * encoding. Here we are not interested in whether we crushed, it
+		 * will work out by anyway because we overwrite the top stone
+		 * type. See (*) later for when we do need to know.
+		 */
 		const uint8_t gaps = A_GET_DATA0(action) & 0x7F,
 			num = A_GET_DATA1(action) & 0x0F, // unpack
 			dir = A_GET_DATA1(action) >> 4;