From 50ec364f5b0be713161ee3ac596ad1c7e10e8940 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Mon, 25 Oct 2021 01:05:19 +0300
Subject: [PATCH] Add blocksum

---
 Makefile   |  2 ++
 blocksum.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 blocksum.c

diff --git a/Makefile b/Makefile
index 951925c..7b8903a 100644
--- a/Makefile
+++ b/Makefile
@@ -5,3 +5,5 @@ era_copy: era_copy.c
 	gcc -o era_copy -Wall era_copy.c
 era_apply: era_apply.c
 	gcc -o era_apply -Wall era_apply.c
+blocksum: blocksum.c
+	gcc -O3 -lssl -lcrypto -o blocksum blocksum.c
diff --git a/blocksum.c b/blocksum.c
new file mode 100644
index 0000000..6c0d556
--- /dev/null
+++ b/blocksum.c
@@ -0,0 +1,60 @@
+/**
+ * Calculates md5 checksums for 4 MB blocks of input
+ *
+ * Author: Vitaliy Filippov <vitalif@yourcmc.ru>, 2021
+ * License: GNU GPLv3.0 or later
+ */
+
+#define _GNU_SOURCE
+#define _LARGEFILE64_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <openssl/md5.h>
+
+int main(int narg, char *args[])
+{
+    int n;
+    MD5_CTX ctx;
+    void *buf = NULL;
+    ssize_t done = 0, r, bufsize = 4*1024*1024, eof = 0;
+    uint64_t pos = 0;
+    unsigned char out[MD5_DIGEST_LENGTH];
+    buf = malloc(bufsize);
+    if (!buf)
+    {
+        fprintf(stderr, "Failed to allocate buffer\n");
+        exit(1);
+    }
+    while (!eof)
+    {
+        MD5_Init(&ctx);
+        while (done < bufsize)
+        {
+            r = read(STDIN_FILENO, buf, bufsize-done);
+            if (r < 0)
+            {
+                eof = 1;
+                break;
+            }
+            if (r > 0)
+            {
+                MD5_Update(&ctx, buf, r);
+                done += r;
+            }
+        }
+        MD5_Final(out, &ctx);
+        printf("%ld ", pos);
+        for (n = 0; n < MD5_DIGEST_LENGTH; n++)
+            printf("%02x", out[n]);
+        printf("\n");
+        pos++;
+        done = 0;
+    }
+    return 0;
+}