crc32

crc32.c

#/* \
make -C "$(dirname "$0")" -f "$0" "$@"; exit $?
crc32: LDLIBS += -lz
crc32: crc32.o
	$(CC) $(LDFLAGS) $(TARGET_ARCH) $^ $(LOADLIBES) $(LDLIBS) -o $@
crc32.o: crc32.c
	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -o $@ $^
help:
	$(info )
	$(info http://www.linuxquestions.org/questions/linux-newbie-8/how-do-i-generate-a-crc32-checksum-163908/#post4670222)
	$(info http://xrefactor.com/blog/polyglot-in-c-makefile-and-shell-script)
	$(info )
.PHONY: help
#*/
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>
#include <zlib.h>
	static int checksum_file(int fd, const char *name) {
	    char buffer[1 << 20];
	    int rc;
	    uLong crc = crc32(0L, Z_NULL, 0);
	    while ((rc = read(fd, buffer, sizeof(buffer))) > 0 ||
	            errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
	        if (rc > 0)
	            crc = crc32(crc, buffer, rc);
	    printf("%08x\t%s\n", crc, name);
	    return rc;
	}
	int main(int argc, const char *const *argv) {
	    int rc = 0;
	    if (argc <= 1)
	        rc = checksum_file(0, "-");
	    else {
	        int i;
	        for (i = 1; !rc && i < argc; i++) {
	            int fd = open(argv[i], O_RDONLY);
	            if (fd < 0)
	                goto err;
	            rc = checksum_file(fd, argv[i]);
	            close(fd);
	            if (rc)
	                break;
	        }
	    }
	    if (!rc)
	        return EX_OK;
	err:
	    fprintf(stderr, "%s\n", strerror(errno));
	    return EX_IOERR;
	}