transpose.c

transpose.c

#include <stdio.h>

/*
 * transpose8x8(p, q):
 *
 * Transpose an 8x8 matrix of boolean values.
 * The transpose operation switches rows into columns and vice versa.
 * The booleans are represented with 1 bit each and packed into 8 bytes
 * for a total of 64 bits.
 *
 * For example, the input array:
 *            p = {0x04, 0xFF, 0x84, 0x84, 0x04, 0x04, 0x04, 0x04}
 * results in q = {0x02, 0x02, 0xFF, 0x02, 0x02, 0x02, 0x02, 0x0E}
 *
 * Because:
 *
 * p[n] | 01234567          q[n] | 01234567
 * -----+------------------------+-----------------
 * 0x04 | --a-----          0x02 | -b------
 * 0xFF | bcdefghi          0x02 | -c------
 * 0x84 | --j----k          0xFF | adjlnopq
 * 0x84 | --l----m   ===>   0x02 | -e------
 * 0x04 | --n-----   ===>   0x02 | -f------
 * 0x04 | --o-----          0x02 | -g------
 * 0x04 | --p-----          0x02 | -h------
 * 0x04 | --q-----          0x0E | -ikm----
 */
void
transpose8x8(unsigned char p[8], unsigned char q[8])
{
	/* your code here */
}


int
main(int argc, char **argv)
{
	unsigned char p[8] = { 0x04, 0xFF, 0x84, 0x84, 0x04, 0x04, 0x04, 0x04 };
	unsigned char q[8] = { 0 };

	transpose8x8(p, q);

	/* draw some ascii art to stdout */
	for (int m = 0; m < 8; m++) {
		printf("%02X ", p[m]);
		for (int n = 0; n < 8; n++) {
			printf("%c", (p[m] >> n) & 1 ? '#' : '-');
		}
		printf("  %02X ", q[m]);
		for (int n = 0; n < 8; n++) {
			printf("%c", (q[m] >> n) & 1 ? '#' : '-');
		}
		printf("\n");
	}
}