111 lines
2.5 KiB
C
111 lines
2.5 KiB
C
/*
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* gf_add.c
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*
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* Adds two numbers in gf_2^w
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*/
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#include <stdio.h>
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#include <getopt.h>
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#include <stdint.h>
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#include <string.h>
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#include <stdlib.h>
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void usage(char *s)
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{
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fprintf(stderr, "usage: gf_add a b w - does addition of a and b in GF(2^w)\n");
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fprintf(stderr, " If w has an h on the end, treat a, b and the sum as hexadecimal (no 0x required)\n");
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fprintf(stderr, "\n");
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fprintf(stderr, " legal w are: 1-32, 64 and 128\n");
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fprintf(stderr, " 128 is hex only (i.e. '128' will be an error - do '128h')\n");
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if (s != NULL) fprintf(stderr, "%s", s);
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exit(1);
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}
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int read_128(char *s, uint64_t *v)
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{
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int l, t;
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char save;
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l = strlen(s);
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if (l > 32) return 0;
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if (l > 16) {
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if (sscanf(s + (l-16), "%llx", (long long unsigned int *) &(v[1])) == 0) return 0;
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save = s[l-16];
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s[l-16] = '\0';
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t = sscanf(s, "%llx", (long long unsigned int *) &(v[0]));
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s[l-16] = save;
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return t;
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} else {
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v[0] = 0;
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return sscanf(s, "%llx", (long long unsigned int *)&(v[1]));
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}
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return 1;
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}
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void print_128(uint64_t *v)
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{
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if (v[0] > 0) {
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printf("%llx", (long long unsigned int) v[0]);
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printf("%016llx", (long long unsigned int) v[1]);
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} else {
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printf("%llx", (long long unsigned int) v[1]);
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}
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printf("\n");
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}
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int main(int argc, char **argv)
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{
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int hex, al, bl, w;
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uint32_t a, b, c, top;
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uint64_t a64, b64, c64;
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uint64_t a128[2], b128[2], c128[2];
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char *format;
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if (argc != 4) usage(NULL);
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if (sscanf(argv[3], "%d", &w) == 0) usage("Bad w\n");
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if (w <= 0 || (w > 32 && w != 64 && w != 128)) usage("Bad w");
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hex = (strchr(argv[3], 'h') != NULL);
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if (!hex && w == 128) usage(NULL);
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if (w <= 32) {
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format = (hex) ? "%x" : "%u";
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if (sscanf(argv[1], format, &a) == 0) usage("Bad a\n");
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if (sscanf(argv[2], format, &b) == 0) usage("Bad b\n");
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if (w < 32) {
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top = (w == 31) ? 0x80000000 : (1 << w);
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if (w != 32 && a >= top) usage("a is too large\n");
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if (w != 32 && b >= top) usage("b is too large\n");
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}
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c = a ^ b;
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printf(format, c);
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printf("\n");
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} else if (w == 64) {
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format = (hex) ? "%llx" : "%llu";
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if (sscanf(argv[1], format, &a64) == 0) usage("Bad a\n");
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if (sscanf(argv[2], format, &b64) == 0) usage("Bad b\n");
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c64 = a64 ^ b64;
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printf(format, c64);
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printf("\n");
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} else if (w == 128) {
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if (read_128(argv[1], a128) == 0) usage("Bad a\n");
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if (read_128(argv[2], b128) == 0) usage("Bad b\n");
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c128[0] = a128[0] ^ b128[0];
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c128[1] = a128[1] ^ b128[1];
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print_128(c128);
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}
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exit(0);
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}
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