1 files changed, 30 insertions, 41 deletions

diff --git a/22.c b/22.c
index 83da420..2a47a79 100644
--- a/22.c
+++ b/22.c
@@ -40,7 +40,8 @@ direction_name(enum direction dir)
 
 
 struct elf {
-	long pos;
+	int x;
+	int y;
 	enum direction dir;
 };
 
@@ -86,46 +87,33 @@ int
 elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type mtype, int distance)
 {
 	while (distance > 0) {
-		int skip, wrap, base;
+		int dx = 0, dy = 0, elem;
 		struct elf newelf;
 
 		switch (elf->dir) {
-		case D_NORTH:
-			skip = -cols;
-			wrap = cols * rows;
-			break;
-
-		case D_EAST:
-			skip = 1;
-			wrap = cols;
-			break;
-
-		case D_SOUTH:
-			skip = cols;
-			wrap = cols * rows;
-			break;
-
-		case D_WEST:
-			skip = -1;
-			wrap = cols;
-			break;
-
+		case D_NORTH: dy = -1; break;
+		case D_SOUTH: dy = +1; break;
+		case D_EAST: dx = +1; break;
+		case D_WEST: dx = -1; break;
 		default:
 			fprintf(stderr, "Unexpected direction %d\n", elf->dir);
 			return -1;
 		}
 
-		base = (elf->pos / wrap) * wrap;
-
-		newelf.pos = base + modulo(elf->pos + skip, wrap);
+		newelf.x = modulo(elf->x + dx, cols);
+		newelf.y = modulo(elf->y + dy, rows);
 		newelf.dir = elf->dir;
+		elem = map[newelf.x + newelf.y * cols];
 
-		if (map[newelf.pos] == ' ' || map[newelf.pos] == '\n') {
+		if (elem == ' ' || elem == '\n') {
 			switch (mtype) {
 			case M_FLAT:
 				// Just keep going until we wrap around to a non-blank position
-				while (map[newelf.pos] == ' ' || map[newelf.pos] == '\n')
-					newelf.pos = base + modulo(newelf.pos + skip, wrap);
+				while (elem == ' ' || elem == '\n') {
+					newelf.x = modulo(newelf.x + dx, cols);
+					newelf.y = modulo(newelf.y + dy, rows);
+					elem = map[newelf.x + newelf.y * cols];
+				}
 				break;
 
 			case M_NET:
@@ -138,7 +126,7 @@ elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type m
 			}
 		}
 
-		switch (map[newelf.pos]) {
+		switch (elem) {
 		case '.':
 			*elf = newelf;
 			--distance;
@@ -149,7 +137,7 @@ elf_move(struct elf * elf, char const * map, int cols, int rows, enum map_type m
 			break;
 
 		default:
-			fprintf(stderr, "Unexpected map character %c\n", map[newelf.pos]);
+			fprintf(stderr, "Unexpected map character %c\n", elem);
 			return -1;
 		}
 	}
@@ -263,13 +251,14 @@ main(int argc, char ** argv)
 	}
 
 	// Set initial position
-	elf.pos = 0;
+	elf.x = 0;
+	elf.y = 0;
 	elf.dir = D_EAST;
-	while (buf[elf.pos] != '.')
-		++elf.pos;
+	while (elf.x < maxline && buf[elf.x] != '.')
+		++elf.x;
 
 	// Read and follow the movement instructions.
-	while (elf.pos >= 0 && (c = fgetc(stdin)) != EOF) {
+	while (elf.x >= 0 && (c = fgetc(stdin)) != EOF) {
 		if (isdigit(c)) {
 			distance[dlen++] = c;
 		}
@@ -277,9 +266,9 @@ main(int argc, char ** argv)
 			distance[dlen] = '\0';
 
 			if (elf_move(&elf, buf, maxline, lines, mtype, atoi(distance)) != 0)
-				elf.pos = -1;
+				elf.x = -1;
 			if (elf_turn(&elf, c) != 0)
-				elf.pos = -1;
+				elf.x = -1;
 
 			dlen = 0;
 		}
@@ -287,7 +276,7 @@ main(int argc, char ** argv)
 			// Cover last bit of distance, if any
 			distance[dlen] = '\0';
 			if (elf_move(&elf, buf, maxline, lines, mtype, atoi(distance)) != 0)
-				elf.pos = -1;
+				elf.x = -1;
 			break;
 		}
 		else {
@@ -296,15 +285,15 @@ main(int argc, char ** argv)
 			return -1;
 		}
 	}
-	if (elf.pos < 0) {
+	if (elf.x < 0) {
 		free(buf);
 		return -1;
 	}
 
 	// Done.
-	printf("Password is %ld (%ld,%ld,%d)\n",
-			1000 * (1 + elf.pos / maxline) + 4 * (1 + elf.pos % maxline) + elf.dir,
-			(1 + elf.pos % maxline), (1 + elf.pos / maxline), elf.dir);
+	printf("Password is %d (%d,%d,%d)\n",
+			1000 * (1 + elf.y) + 4 * (1 + elf.x) + elf.dir,
+			1 + elf.x, 1 + elf.y, elf.dir);
 
 	// Tidy and exit.
 	free(buf);