Improve RNG compatibility with old compilers.

[rrace.git] / src / game.c

diff --git a/src/game.c b/src/game.c
index 999d52674abd10007334811ec3a8d8562c40d801..801625103ab9ef09ae747a8a9b3c6447f36645a7 100644 (file)
--- a/src/game.c
+++ b/src/game.c
@@ -1,6 +1,6 @@
 /*
  * Slide puzzle core game logic
- * Copyright © 2022 Nick Bowler
+ * Copyright © 2022-2024 Nick Bowler
  *
  * 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
@@ -23,11 +23,11 @@
 #include <config.h>
 #include <limits.h>
 #include <string.h>
+#include <unistd.h>
 #include <time.h>
-#include <gethrxtime.h>
 #include "game.h"
 
-#define B64(x) ((x) & 0xffffffffffffffff)
+#define B64(x) ((x) & 0xffffffffffffffffull)
 
 /* Rotate val left by n bits.  The behaviour is undefined if n is zero. */
 static unsigned long long rot_left64(unsigned long long val, int n)
@@ -56,9 +56,9 @@ static unsigned long long splitmix64(unsigned long long *state)
 {
        unsigned long long z;
 
-       z = B64(*state += 0x9e3779b97f4a7c15);
-       z = B64((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9);
-       z = B64((z ^ (z >> 27)) * 0x94d049bb133111eb);
+       z = B64(*state += 0x9e3779b97f4a7c15ull);
+       z = B64((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ull);
+       z = B64((z ^ (z >> 27)) * 0x94d049bb133111ebull);
 
        return z ^ (z >> 31);
 }
@@ -119,6 +119,12 @@ void game_reseed(unsigned long long seed)
        rng_state[3] = splitmix64(&seed);
 }
 
+#define assign_tile(planes, tile, bit) do { \
+       0[planes] |= (((tile)>>0) & 1ul) << (bit); \
+       1[planes] |= (((tile)>>1) & 1ul) << (bit); \
+       2[planes] |= (((tile)>>2) & 1ul) << (bit); \
+} while (0)
+
 void game_reset(struct board *board)
 {
        unsigned char tiles[25];
@@ -127,8 +133,19 @@ void game_reset(struct board *board)
        if (!rng_is_seeded()) {
                unsigned long long seed;
 
-               seed = time(NULL);
-               seed += gethrxtime();
+               /*
+                * Try to get a reasonable initial seed.
+                *
+                * Reasonable in this context means:
+                *
+                * - roughly even distribution of 1/0 bits, and
+                * - unlikely to generate the same seed twice in succession.
+                */
+               game_begin(board);
+
+               seed  = time(NULL);
+               seed += board->time_start;
+               seed += (unsigned long long)getpid() << 16;
                seed += seed << 32;
 
                game_reseed(seed);
@@ -141,33 +158,55 @@ void game_reset(struct board *board)
        shuffle(tiles, 24);
        memset(board->goal, 0, sizeof board->goal);
 
-       for (i = 0; i < 9; i++) {
-               uint_fast32_t position = board_position(i/3+1, i%3+1) >> 6;
-
-               if (tiles[i] & 1) board->goal[0] |= position;
-               if (tiles[i] & 2) board->goal[1] |= position;
-               if (tiles[i] & 4) board->goal[2] |= position;
+       /*
+        * Goal bitmap has 2-tile "gaps" between rows; it doesn't matter what
+        * these are set to and since we have a random permutation it doesn't
+        * matter which of the 24 nonempty tiles we pick for the actual goal.
+        */
+       for (i = 0; i < 13; i++) {
+               assign_tile(board->goal, tiles[i], i);
        }
 
        tiles[24] = TILE_EMPTY;
        shuffle(tiles, 25);
-
        memset(board->game, 0, sizeof board->game);
+
        for (i = 0; i < 25; i++) {
-               unsigned x = i/5, y = i%5;
-               uint_fast32_t position;
-
-               position = board_position(x, y);
-               if (tiles[i] != TILE_EMPTY) {
-                       if (tiles[i] & 1) board->game[0] |= position;
-                       if (tiles[i] & 2) board->game[1] |= position;
-                       if (tiles[i] & 4) board->game[2] |= position;
-               } else {
-                       board->game[3] = ~position;
-                       board->x = x;
-                       board->y = y;
+               assign_tile(board->game, tiles[i], i);
+
+               if (tiles[i] == TILE_EMPTY) {
+                       board->game[3] = (1ul<<i);
+                       board->x = i%5;
+                       board->y = i/5;
                }
        }
+
+/* Uncomment to make every game stupidly easy -- winnable in 1 move */
+#if 0
+       /* Force empty space to the border */
+       if (board_position(board->x, board->y) & GOAL_MASK) {
+               switch (rng_uniform_int(4)) {
+               case 0: game_do_move(board, board->x, 0); break;
+               case 1: game_do_move(board, board->x, 4); break;
+               case 2: game_do_move(board, 0, board->y); break;
+               case 3: game_do_move(board, 4, board->y); break;
+               }
+       }
+
+       /* Force goal to match the current board */
+       for (i = 0; i < 3; i++) {
+               board->goal[i] = (board->game[i] & GOAL_MASK) >> GOAL_SHIFT;
+       }
+
+       /* Move empty space back to the centre */
+       if (board->x == 0 || board->x == 4) {
+               game_do_move(board, 1+rng_uniform_int(3), board->y);
+       }
+
+       if (board->y == 0 || board->y == 4) {
+               game_do_move(board, board->x, 1+rng_uniform_int(3));
+       }
+#endif
 }
 
 uint_fast32_t game_do_move(struct board *board, int x, int y)
@@ -209,23 +248,13 @@ uint_fast32_t game_check_goal(struct board *board)
        int i;
 
        for (i = 0; i < 3; i++)
-               mask |= goal[i] ^ (game[i] >> GOAL_SHIFT);
-       return (mask << GOAL_SHIFT) & GOAL_MASK;
-}
-
-void game_begin(struct board *board)
-{
-       board->time_start = gethrxtime();
-}
-
-static int_fast32_t elapsed(struct board *board)
-{
-       return (gethrxtime() - board->time_start) / 1000000;
+               mask |= game[i] ^ ((0ul+goal[i]) << GOAL_SHIFT);
+       return mask & GOAL_MASK;
 }
 
 int_fast32_t game_finish(struct board *board)
 {
-       int_fast32_t t = elapsed(board);
+       int_fast32_t t = game_elapsed(board);
        int i;
 
        for (i = 0; i < 4; i++) {