/*
* GF-Complete: A Comprehensive Open Source Library for Galois Field Arithmetic
* James S. Plank, Ethan L. Miller, Kevin M. Greenan,
* Benjamin A. Arnold, John A. Burnum, Adam W. Disney, Allen C. McBride.
*
*
* Adds two numbers in gf_2^w
*/

#include <stdio.h>
#include <getopt.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>

void usage(char *s)
{
fprintf(stderr, "usage: gf_add a b w - does addition of a and b in GF(2^w)\n");
fprintf(stderr, "       If w has an h on the end, treat a, b and the sum as hexadecimal (no 0x required)\n");
fprintf(stderr, "\n");
fprintf(stderr, "       legal w are: 1-32, 64 and 128\n");
fprintf(stderr, "       128 is hex only (i.e. '128' will be an error - do '128h')\n");

if (s != NULL) fprintf(stderr, "%s", s);
exit(1);
}

int read_128(char *s, uint64_t *v)
{
int l, t;
char save;

l = strlen(s);
if (l > 32) return 0;

if (l > 16) {
if (sscanf(s + (l-16), "%llx", (long long unsigned int *) &(v[1])) == 0) return 0;
save = s[l-16];
s[l-16] = '\0';
t = sscanf(s, "%llx", (long long unsigned int *) &(v[0]));
s[l-16] = save;
return t;
} else {
v[0] = 0;
return sscanf(s, "%llx", (long long unsigned int *)&(v[1]));
}
return 1;
}

void print_128(uint64_t *v)
{
if (v[0] > 0) {
printf("%llx", (long long unsigned int) v[0]);
printf("%016llx", (long long unsigned int) v[1]);
} else {
printf("%llx", (long long unsigned int) v[1]);
}
printf("\n");
}

int main(int argc, char **argv)
{
int hex, w;
uint32_t a, b, c, top;
uint64_t a64, b64, c64;
uint64_t a128[2], b128[2], c128[2];
char *format;

if (argc != 4) usage(NULL);
if (sscanf(argv[3], "%d", &w) == 0) usage("Bad w\n");

if (w <= 0 || (w > 32 && w != 64 && w != 128)) usage("Bad w");

hex = (strchr(argv[3], 'h') != NULL);

if (!hex && w == 128) usage(NULL);

if (w <= 32) {
format = (hex) ? "%x" : "%u";
if (sscanf(argv[1], format, &a) == 0) usage("Bad a\n");
if (sscanf(argv[2], format, &b) == 0) usage("Bad b\n");

if (w < 32) {
top = (w == 31) ? 0x80000000 : (1 << w);
if (w != 32 && a >= top) usage("a is too large\n");
if (w != 32 && b >= top) usage("b is too large\n");
}

c = a ^ b;
printf(format, c);
printf("\n");

} else if (w == 64) {
format = (hex) ? "%llx" : "%llu";
if (sscanf(argv[1], format, &a64) == 0) usage("Bad a\n");
if (sscanf(argv[2], format, &b64) == 0) usage("Bad b\n");
c64 = a64 ^ b64;

printf(format, c64);
printf("\n");

} else if (w == 128) {

if (read_128(argv[1], a128) == 0) usage("Bad a\n");
if (read_128(argv[2], b128) == 0) usage("Bad b\n");
c128[0] = a128[0] ^ b128[0];
c128[1] = a128[1] ^ b128[1];

print_128(c128);
}
exit(0);
}