From 2391e74bd29ee62c00472f60260c4e07770e7b9c Mon Sep 17 00:00:00 2001
From: Paul Gardner-Stephen <paul@servalproject.org>
Date: Wed, 24 Apr 2019 09:20:53 +0930
Subject: [PATCH] begin implementing similarity comparison tool.

---
 Makefile         |  3 ++
 src/similarity.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 src/similarity.c

diff --git a/Makefile b/Makefile
index cb7fb9db..b7cdd314 100644
--- a/Makefile
+++ b/Makefile
@@ -6,6 +6,9 @@ src/collect_data:	src/collect_data.c Makefile
 src/preprocess:	src/preprocess.c Makefile
 	gcc -g -Wall -o src/preprocess src/preprocess.c
 
+src/similarity:	src/similarity.c Makefile
+	gcc -g -Wall -o src/similarity src/similarity.c
+
 src/make_error_tables:	src/make_error_tables.c Makefile
 	gcc -g -Wall -o src/make_error_tables src/make_error_tables.c
 
diff --git a/src/similarity.c b/src/similarity.c
new file mode 100644
index 00000000..5ea97635
--- /dev/null
+++ b/src/similarity.c
@@ -0,0 +1,82 @@
+/*
+  Simple program to find matching strings between two binaries
+  and report on the statistics of their lengths, and show the
+  longer ones. Used to defend against copyright infringement
+  claims.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <strings.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define MAX_SIZE 8192
+int matches[MAX_SIZE];
+
+int main(int argc,char **argv)
+{
+  if (argc!=3) {
+    fprintf(stderr,"usage: similarity <file1> <file2>\n");
+    exit(-1);
+  }
+
+  for(int i=0;i<MAX_SIZE;i++) matches[i]=0;
+
+  unsigned char *f1,*f2;
+  int s1,s2;
+  struct stat st;
+  int fd;
+
+  fd = open(argv[1], O_RDONLY, 0);
+  if (fd==-1) {
+    fprintf(stderr,"Could not read '%s'\n",argv[1]);
+    exit(-1);
+  }
+  stat(argv[1], &st);
+  s1=st.st_size;
+  f1 = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE | MAP_POPULATE, fd, 0);
+  if (f1== MAP_FAILED) {
+    fprintf(stderr,"Could not mmap '%s'\n",argv[1]);
+    exit(-1);
+  }
+  fd = open(argv[2], O_RDONLY, 0);
+  if (fd==-1) {
+    fprintf(stderr,"Could not read '%s'\n",argv[2]);
+    exit(-1);
+  }
+  stat(argv[2], &st);
+  s2=st.st_size;
+  f2 = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE | MAP_POPULATE, fd, 0);
+  if (f2 == MAP_FAILED) {
+    fprintf(stderr,"Could not mmap '%s'\n",argv[2]);
+    exit(-1);
+  }
+
+  fprintf(stderr,"Searching files for similarities...\n");
+  
+  for(int i=0;i<s1;i++) {
+    for(int j=0;j<s2;j++) {
+      int k,l;
+      for(k=0;((i+k)<s1)&&((j+k)<s2);k++)
+	if (f1[i+k]!=f2[j+k]) break;
+      // Ignore matches that are all the same byte
+      for(l=1;l<k;l++) if (f1[i+l]!=f1[i]) break;
+      if (l<k) {
+	if (k) matches[k]++;
+      }
+     
+    }
+  }
+
+  for(int i=0;i<MAX_SIZE;i++) {
+    if (matches[i])
+      printf("%6d matches of %d bytes\n",matches[i],i);
+  }
+  
+  return 0;
+}