#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>   /* for perror() */
#include <string.h>  /* for memcpy() */
#include <stdlib.h>  /* for realloc(), free() */
#include <unistd.h>  /* for write() */

#define LM_ARRAY_LEN(ary)       (sizeof(ary)/sizeof((ary)[0]))
#define LM_CEILDIV(n, d)        ( ((n)+(d)-1) / (d) )
#define LM_NEXT_POWER_OF_2(x)   ( (x) ? 1ULL<<((sizeof(unsigned long long)*8)-__builtin_clzll(x)) : 1)
#define LM_CAT2(a, b)           a ## b
#define LM_CAT2_(a, b)          LM_CAT2(a, b)
#define assert_notreached(msg)  assert(false)

struct buf {
	uint8_t *dat;
	size_t   len;
	size_t   cap;
};

static void append(struct buf *buf, void *dat, size_t len) {
	assert(buf);
	assert(len == 0 || dat);

	if (buf->len + len > buf->cap) {
		buf->cap = LM_NEXT_POWER_OF_2(buf->len + len);
		buf->dat = realloc(buf->dat, buf->cap);
		assert(buf->dat);
	}
	memcpy(&buf->dat[buf->len], dat, len);
	buf->len += len;
}

static void append_u32be(struct buf *buf, uint32_t val) {
	assert(buf);

	uint8_t dat[4] = {
		(val>>(8*3))&0xFF,
		(val>>(8*2))&0xFF,
		(val>>(8*1))&0xFF,
		(val>>(8*0))&0xFF,
	};
	append(buf, dat, sizeof(dat));
}

static bool xwrite(int fd, uint8_t *dat, size_t len) {
	assert(len == 0 || dat);

	for (size_t done = 0; done < len;) {
		ssize_t n = write(fd, &dat[done], len-done);
		if (n < 0) {
			perror("write");
			return true;
		}
		done += n;
	}
	return false;
}

static char font[10][8*4] = {
	"   ##   "
	"  #  #  "
	"  #  #  "
	"   ##   ",

	"    #   "
	"   ##   "
	"    #   "
	"   ###  ",

	"   ##   "
	"  #  #  "
	"    #   "
	"  ####  ",

	"   ##   "
	"     #  "
	"     #  "
	"   ##   ",

	"    ##  "
	"   # #  "
	"  ####  "
	"     #  ",

	"  ####  "
	"  ###   "
	"     #  "
	"  ###   ",

	"  #     "
	"  ###   "
	"  #  #  "
	"   ##   ",

	"  ####  "
	"    #   "
	"   #    "
	"   #    ",

	"   ##   "
	"  #  #  "
	"  ####  "
	"   ##   ",

	"   ##   "
	"  #  #  "
	"   ###  "
	"     #  ",
};
static_assert(LM_ARRAY_LEN(font) == 10);
static_assert(sizeof(font[0]) == 32);