initial commit

1 files changed, 53 insertions, 0 deletions

diff --git a/src/alfsum.c b/src/alfsum.c
new file mode 100644
index 0000000..7f30c7c
--- /dev/null
+++ b/src/alfsum.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <unistd.h>
+
+/* 20251104 bkw: implement the simple checksum used by ALF.
+   Dumbest possible algo: all the bytes are added together and
+   the bottom 16 bits of the result is the checksum. */
+
+char *self;
+
+void alfsum(const char *file, FILE *f) {
+	int c;
+	unsigned long sum = 0;
+
+	while((c = fgetc(f)) != EOF)
+		sum += c;
+
+	printf("%8s\t%04x\n", file, (unsigned int)(sum & 0xffff));
+}
+
+int main(int argc, char **argv) {
+	int errs = 0;
+	char *file;
+	FILE *f;
+
+	self = argv[0];
+
+	/* if the first arg is a - followed by anything at all, assume --help */
+	if(argc < 2 || (argc == 2 && argv[1][0] == '-' && argv[1][1])) {
+		fprintf(stderr,
+				"usage: %s filename [filename ...]\n"
+				"\t(use - to read from standard input)\n",
+				self);
+		return -1;
+	}
+
+	while((file = *++argv)) {
+		if(argv[0][0] == '-' && !argv[0][1]) {
+			if(isatty(0))
+				fprintf(stderr, "%s: reading from stdin...\n", self);
+			f = stdin;
+			file = " (stdin)";
+		} else if(!(f = fopen(file, "rb"))) {
+			fprintf(stderr, "%s: ", self);
+			perror(file);
+			errs++;
+			continue;
+		}
+		alfsum(file, f);
+		fclose(f);
+	}
+
+	return errs > 254 ? 254 : errs;
+}