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ctz.c
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ctz.c
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/*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
* Copyright (C) 2018 Stefan Teleman.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
void print_help(void)
{
(void) fprintf(stderr, "Usage: ctz -v <value> [-b <bits> (default 64)]\n"
" [-p (print bitmask)]\n");
}
void print_bitmask(uint64_t x, int bits)
{
(void) fprintf(stderr, "%lu: [", x);
for (int i = 0; i < bits; ++i) {
if (x & (1UL << (uint64_t) i))
(void) fprintf(stdout, "1");
else
(void) fprintf(stdout, "0");
}
(void) fprintf(stdout, "]\n");
}
uint32_t ctz64(uint64_t x)
{
for (int i = 63; i >= 0; --i) {
if (x & (1UL << (uint64_t) i))
return 63 - i;
}
return 64;
}
uint32_t ctz32(uint32_t x)
{
for (int i = 31; i >= 0; --i) {
if (x & (1U << (uint32_t) i))
return 31 - i;
}
return 32;
}
int main(int argc, char* argv[])
{
int opt;
int bits = 64;
uint64_t x = 0;
bool pb = false;
bool ph = false;
while ((opt = getopt(argc, argv, "pb:v:")) != -1) {
switch (opt) {
case 'p':
pb = true;
break;
case 'b':
bits = (unsigned) strtoul(optarg, NULL, 10);
break;
case 'v':
x = strtoul(optarg, NULL, 10);
break;
default:
ph = true;
break;
}
}
if (ph || argc < 3) {
print_help();
return 1;
}
if (pb)
print_bitmask(x, bits);
if (bits == 32)
(void) fprintf(stdout, "%u\n", ctz32((uint32_t) x));
else
(void) fprintf(stdout, "%u\n", ctz64(x));
return 0;
}