From 08a13cd9759451ccf298000448ad52513a451dfe Mon Sep 17 00:00:00 2001
From: Werner Almesberger <werner@almesberger.net>
Date: Wed, 17 Aug 2011 06:59:05 -0300
Subject: [PATCH] bitcmp/: little utility to find which bits differ between two
 files

---
 bitcmp/Makefile |   3 ++
 bitcmp/bitcmp.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 bitcmp/Makefile
 create mode 100644 bitcmp/bitcmp.c

diff --git a/bitcmp/Makefile b/bitcmp/Makefile
new file mode 100644
index 0000000..304914c
--- /dev/null
+++ b/bitcmp/Makefile
@@ -0,0 +1,3 @@
+CFLAGS=-Wall
+
+all:	bitcmp
diff --git a/bitcmp/bitcmp.c b/bitcmp/bitcmp.c
new file mode 100644
index 0000000..2ed76d4
--- /dev/null
+++ b/bitcmp/bitcmp.c
@@ -0,0 +1,125 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <fcntl.h>
+
+
+#define	BUFFER	4096
+
+
+static int do_open(const char *name)
+{
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd >= 0)
+		return fd;
+
+	perror(name);
+	exit(1);
+}
+
+
+static void usage(const char *name)
+{
+	fprintf(stderr,
+"usage: %s [-w|-l] [-B] file1 file2\n"
+"  -w  compare words (16 bits; default is bytes)\n"
+"  -l  compare long words (32 bits; default is bytes)\n"
+"  -B  use big-endian (default: little-endian)\n"
+    , name);
+	exit(1);
+}
+
+
+int main(int argc, char *const *argv)
+{
+	int little = 1;
+	int bytes = 1;
+	int c;
+	int fd1, fd2;
+	const char *name1, *name2;
+	uint8_t buf1[BUFFER], buf2[BUFFER];
+	ssize_t got1, got2, len;
+	uint32_t diff;
+	int i, j;
+	static unsigned bin[32];
+
+	while ((c = getopt(argc, argv, "Blw")) != EOF) {
+		switch (c) {
+		case 'B':
+			little = 0;
+			break;
+		case 'l':
+			bytes = 4;
+			break;
+		case 'w':
+			bytes = 2;
+			break;
+		default:
+			usage(*argv);
+		}
+	}
+	if (argc-optind != 2)
+		usage(*argv);
+
+	name1 = argv[optind];
+	name2 = argv[optind+1];
+
+	fd1 = do_open(name1);
+	fd2 = do_open(name2);
+
+	while (1) {
+		memset(buf1, 0, BUFFER);
+		memset(buf2, 0, BUFFER);
+		got1 = read(fd1, buf1, BUFFER);
+		if (got1 < 0) {
+			perror(name1);
+			return 1;
+		}
+		got2 = read(fd2, buf2, BUFFER);
+		if (got2 < 0) {
+			perror(name2);
+			return 1;
+		}
+		if (got1 != got2)
+			fprintf(stderr, "%s < %s\n",
+			    got1 < got2 ? name1 : name2,
+			    got1 < got2 ? name2 : name1);
+		len = got1 < got2 ? got1 : got2;
+		if (!len)
+			break;
+		for (i = 0; i <= len; i += bytes) {
+			diff = 0;
+			switch (bytes) {
+			case 4:
+				diff |= (buf1[i+2] ^ buf2[i+2]) << 16;
+				diff |= (buf1[i+3] ^ buf2[i+3]) << 24;
+				/* fall through */
+			case 2:
+				diff |= (buf1[i+1] ^ buf2[i+1]) << 8;
+				/* fall through */
+			case 1:
+				diff |= buf1[i] ^ buf2[i];
+				break;
+			default:
+				abort();
+			}
+			for (j = 0; j != 32; j++)
+				if (diff & (1 << j))
+					bin[j]++;
+		}
+	}
+
+	for (j = 0; j != 8*bytes; j++) {
+		if (little)
+			i = j;
+		else
+			i = 8*(bytes-1-(j >> 3))+(j & 7);
+		if (bin[i])
+			printf("%2d: %u\n", j, bin[i]);
+	}
+	return 0;
+}