From 2dca1af44806924946828e2fdc82ea408353d286 Mon Sep 17 00:00:00 2001
From: Nicolas Pitre <nico@cam.org>
Date: Wed, 11 Apr 2007 13:59:51 -0400
Subject: [PATCH] simple random data generator for tests

Reliance on /dev/urandom produces test vectors that are, well, random.
This can cause problems impossible to track down when the data is
different from one test invokation to another.

The goal is not to have random data to test, but rather to have a
convenient way to create sets of large files with non compressible and
non deltifiable data in a reproducible way.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
---
 .gitignore       |  1 +
 Makefile         |  7 +++++--
 test-genrandom.c | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 test-genrandom.c

diff --git a/.gitignore b/.gitignore
index 9229e918c..fa7ac9359 100644
--- a/.gitignore
+++ b/.gitignore
@@ -149,6 +149,7 @@ test-chmtime
 test-date
 test-delta
 test-dump-cache-tree
+test-genrandom
 test-match-trees
 common-cmds.h
 *.tar.gz
diff --git a/Makefile b/Makefile
index a77d31de9..bd0ba95b1 100644
--- a/Makefile
+++ b/Makefile
@@ -932,7 +932,7 @@ endif
 
 export NO_SVN_TESTS
 
-test: all test-chmtime$X
+test: all test-chmtime$X test-genrandom$X
 	$(MAKE) -C t/ all
 
 test-date$X: test-date.c date.o ctype.o
@@ -953,6 +953,9 @@ test-match-trees$X: test-match-trees.o $(GITLIBS)
 test-chmtime$X: test-chmtime.c
 	$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $<
 
+test-genrandom$X: test-genrandom.c
+	$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $<
+
 check-sha1:: test-sha1$X
 	./test-sha1.sh
 
@@ -1041,7 +1044,7 @@ dist-doc:
 
 clean:
 	rm -f *.o mozilla-sha1/*.o arm/*.o ppc/*.o compat/*.o xdiff/*.o \
-		test-chmtime$X $(LIB_FILE) $(XDIFF_LIB)
+		test-chmtime$X test-genrandom$X $(LIB_FILE) $(XDIFF_LIB)
 	rm -f $(ALL_PROGRAMS) $(BUILT_INS) git$X
 	rm -f *.spec *.pyc *.pyo */*.pyc */*.pyo common-cmds.h TAGS tags
 	rm -rf autom4te.cache
diff --git a/test-genrandom.c b/test-genrandom.c
new file mode 100644
index 000000000..8cefe6cfe
--- /dev/null
+++ b/test-genrandom.c
@@ -0,0 +1,34 @@
+/*
+ * Simple random data generator used to create reproducible test files.
+ * This is inspired from POSIX.1-2001 implementation example for rand().
+ * Copyright (C) 2007 by Nicolas Pitre, licensed under the GPL version 2.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+	unsigned long count, next = 0;
+	unsigned char *c;
+
+	if (argc < 2 || argc > 3) {
+		fprintf( stderr, "Usage: %s <seed_string> [<size>]", argv[0]);
+		return 1;
+	}
+
+	c = (unsigned char *) argv[1];
+	do {
+		next = next * 11 + *c;
+	} while (*c++);
+
+	count = (argc == 3) ? strtoul(argv[2], NULL, 0) : -1L;
+
+	while (count--) {
+		next = next * 1103515245 + 12345;
+		if (putchar((next >> 16) & 0xff) == EOF)
+			return -1;
+	}
+
+	return 0;
+}
-- 
2.30.2