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Small fix for snake example (#13790)

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Rename THREE_BITS to SNAKE_CELL_SET_BITS
Make SNAKE_CELL_SET_BITS depend on SNAKE_CELL_MAX_BITS
This commit is contained in:
Marcus Harrison
2025-08-27 14:16:24 +02:00
committed by GitHub
parent 0bbdd86b86
commit b795762b62
1 changed files with 5 additions and 6 deletions
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11
examples/demo/01-snake/snake.c
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@@ -18,7 +18,8 @@
#define SNAKE_GAME_HEIGHT 18U
#define SNAKE_MATRIX_SIZE (SNAKE_GAME_WIDTH * SNAKE_GAME_HEIGHT)
#define THREE_BITS 0x7U /* ~CHAR_MAX >> (CHAR_BIT - SNAKE_CELL_MAX_BITS) */
#define SNAKE_CELL_MAX_BITS 3U /* floor(log2(SNAKE_CELL_FOOD)) + 1 */
#define SNAKE_CELL_SET_BITS (~(~0u << SNAKE_CELL_MAX_BITS))
#define SHIFT(x, y) (((x) + ((y) * SNAKE_GAME_WIDTH)) * SNAKE_CELL_MAX_BITS)
static SDL_Joystick *joystick = NULL;
@@ -33,8 +34,6 @@ typedef enum
SNAKE_CELL_FOOD = 5U
} SnakeCell;
#define SNAKE_CELL_MAX_BITS 3U /* floor(log2(SNAKE_CELL_FOOD)) + 1 */
typedef enum
{
SNAKE_DIR_RIGHT,
@@ -68,7 +67,7 @@ SnakeCell snake_cell_at(const SnakeContext *ctx, char x, char y)
const int shift = SHIFT(x, y);
unsigned short range;
SDL_memcpy(&range, ctx->cells + (shift / 8), sizeof(range));
return (SnakeCell)((range >> (shift % 8)) & THREE_BITS);
return (SnakeCell)((range >> (shift % 8)) & SNAKE_CELL_SET_BITS);
}
static void set_rect_xy_(SDL_FRect *r, short x, short y)
@@ -84,8 +83,8 @@ static void put_cell_at_(SnakeContext *ctx, char x, char y, SnakeCell ct)
unsigned char *const pos = ctx->cells + (shift / 8);
unsigned short range;
SDL_memcpy(&range, pos, sizeof(range));
range &= ~(THREE_BITS << adjust); /* clear bits */
range |= (ct & THREE_BITS) << adjust;
range &= ~(SNAKE_CELL_SET_BITS << adjust); /* clear bits */
range |= (ct & SNAKE_CELL_SET_BITS) << adjust;
SDL_memcpy(pos, &range, sizeof(range));
}