diff -r 6008840b859e -r 6a26114297a1 src/chess/knight.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/chess/knight.c	Mon Mar 31 11:16:32 2014 +0200
@@ -0,0 +1,133 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2014 Mike Becker. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "knight.h"
+#include "rules.h"
+#include <stdlib.h>
+
+_Bool knight_chkrules(Move *move) {
+    int dx = abs(move->fromfile - move->tofile);
+    int dy = abs(move->fromrow - move->torow);
+    
+    return (dx == 2 && dy == 1) || (dx == 1 && dy == 2);
+}
+
+static int knight_getloc_fixedrow(Board board, Move *move) {
+    int d = 3 - abs(move->fromrow - move->torow);
+    
+    if (d == 1 || d == 2) {
+        if (move->tofile < 6 &&
+            board[move->fromrow][move->tofile + d] == move->piece) {
+            if (move->fromfile == POS_UNSPECIFIED) {
+                move->fromfile = move->tofile + d;
+                return VALID_MOVE_SYNTAX;
+            } else {
+                return AMBIGUOUS_MOVE;
+            }
+        }
+        if (move->tofile > 1 &&
+            board[move->fromrow][move->tofile - d] == move->piece) {
+            if (move->fromfile == POS_UNSPECIFIED) {
+                move->fromfile = move->tofile - d;
+                return VALID_MOVE_SYNTAX;
+            } else {
+                return AMBIGUOUS_MOVE;
+            }
+        }
+    }
+    
+    return INVALID_POSITION;
+}
+
+static int knight_getloc_fixedfile(Board board, Move *move) {
+    int d = 3 - abs(move->fromfile - move->tofile);
+    
+    if (d == 1 || d == 2) {
+        if (move->torow < 6 &&
+            board[move->torow + d][move->fromfile] == move->piece) {
+            if (move->fromrow == POS_UNSPECIFIED) {
+                move->fromrow = move->torow + d;
+                return VALID_MOVE_SYNTAX;
+            } else {
+                return AMBIGUOUS_MOVE;
+            }
+        }
+        if (move->torow > 1 &&
+            board[move->torow - d][move->fromfile] == move->piece) {
+            if (move->fromrow == POS_UNSPECIFIED) {
+                move->fromrow = move->torow - d;
+                return VALID_MOVE_SYNTAX;
+            } else {
+                return AMBIGUOUS_MOVE;
+            }
+        }
+    }
+    
+    return INVALID_POSITION;
+}
+
+int knight_getlocation(Board board, Move *move) {
+    
+    if (move->fromfile != POS_UNSPECIFIED) {
+        return knight_getloc_fixedfile(board, move);
+    }
+    
+    if (move->fromrow != POS_UNSPECIFIED) {
+        return knight_getloc_fixedrow(board, move);
+    }
+    
+    for (int x = -2 ; x <= 2 ; x++) {
+        if (x == 0) {
+            continue;
+        }
+        for (int y = -2 ; y <= 2 ; y++) {
+            if (y == 0 || y == x) {
+                continue;
+            }
+            uint8_t cx = move->tofile + x;
+            uint8_t cy = move->torow + y;
+
+            if (isidx(cx) && isidx(cy) && board[cy][cx] == move->piece) {
+                if (move->fromfile == POS_UNSPECIFIED
+                    && move->fromrow == POS_UNSPECIFIED) {
+                    move->fromfile = cx;
+                    move->fromrow = cy;
+                } else {
+                    return AMBIGUOUS_MOVE;
+                }
+            }
+        }
+    }
+    
+    if (move->fromfile == POS_UNSPECIFIED || move->fromrow == POS_UNSPECIFIED) {
+        return INVALID_POSITION;
+    } else {
+        return VALID_MOVE_SYNTAX;
+    }
+}