--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/miscprog/pircksum2.c	Sun Dec 25 23:48:16 2016 +0000
@@ -0,0 +1,116 @@
+/*
+ * This program verifies the correctness of the understanding described in the
+ * ../pirelli/flash2-chksum write-up.
+ */
+
+#include <sys/types.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <endian.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+char *image_filename;
+u_char *image_map, *endrec;
+unsigned imgsize, max_imgsize;
+
+open_and_map_file()
+{
+	int fd;
+	struct stat st;
+
+	fd = open(image_filename, O_RDONLY);
+	if (fd < 0) {
+		perror(image_filename);
+		exit(1);
+	}
+	fstat(fd, &st);
+	if (!S_ISREG(st.st_mode)) {
+		fprintf(stderr, "error: %s is not a regular file\n",
+			image_filename);
+		exit(1);
+	}
+	if (st.st_size != 0x10000 && st.st_size != 0x360000) {
+		fprintf(stderr, "error: %s has an unexpected size\n",
+			image_filename);
+		exit(1);
+	}
+	max_imgsize = st.st_size - 12;
+	image_map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (image_map == MAP_FAILED) {
+		perror("mmap");
+		exit(1);
+	}
+	close(fd);
+	endrec = image_map + max_imgsize;
+	return 0;
+}
+
+verify_chksum1()
+{
+	uint16_t sum, ref;
+	unsigned offset;
+
+	sum = 0;
+	for (offset = 0; offset + 1 < imgsize; offset += 2)
+		sum += le16toh(*(uint16_t *)(image_map + offset));
+	if (imgsize & 1)
+		sum += image_map[offset];
+	ref = le16toh(*(uint16_t *)(endrec + 8));
+	if (sum == ref) {
+		printf("Checksum 1 matches (%04X)\n", sum);
+		return 0;
+	} else {
+		printf("Checksum 1 FAILED: computed %04X, stored %04X\n",
+			sum, ref);
+		return 1;
+	}
+}
+
+verify_chksum2()
+{
+	uint16_t sum, ref;
+	unsigned offset;
+
+	sum = 0;
+	for (offset = 0; offset < 10; offset += 2)
+		sum += le16toh(*(uint16_t *)(endrec + offset));
+	ref = le16toh(*(uint16_t *)(endrec + 10));
+	if (sum == ref) {
+		printf("Checksum 2 matches (%04X)\n", sum);
+		return 0;
+	} else {
+		printf("Checksum 2 FAILED: computed %04X, stored %04X\n",
+			sum, ref);
+		return 1;
+	}
+}
+
+main(argc, argv)
+	char **argv;
+{
+	int stat1, stat2;
+
+	if (argc != 2) {
+		fprintf(stderr, "usage: %s image-filename\n", argv[0]);
+		exit(1);
+	}
+	image_filename = argv[1];
+	open_and_map_file();
+	if (le32toh(*(uint32_t *)endrec) != 0x12345678) {
+		printf("Error: 0x12345678 signature missing\n");
+		exit(1);
+	}
+	imgsize = le32toh(*(uint32_t *)(endrec + 4));
+	if (imgsize < 1 || imgsize > max_imgsize) {
+		printf("Error: bogus image size of 0x%x bytes\n", imgsize);
+		exit(1);
+	}
+	printf("Image size: 0x%x bytes\n", imgsize);
+	stat1 = verify_chksum1();
+	stat2 = verify_chksum2();
+	exit(stat1 || stat2);
+}