Add tests for libdeflate_zlib_*

Adds programs/test_zlib.c which currently does the following:
1. Create some dummy data and compress it
2. Try to decompress with libdeflate_zlib_decompress
3. Try to decompress with libdeflate_zlib_decompress, with unnecessary
   trailing bytes after the compressed data
4. Try to decompress with libdeflate_zlib_decompress_ex, with
   unnecessary trailing bytes after the compressed data

In each step, we check that we get back the original data.

Makefile

@@ -216,7 +216,8 @@ TEST_PROG_SRC        := programs/benchmark.c \
 			programs/checksum.c \
 			programs/test_checksums.c \
 			programs/test_incomplete_codes.c \
-			programs/test_slow_decompression.c
+			programs/test_slow_decompression.c \
+			programs/test_zlib.c
 
 NONTEST_PROGRAMS := $(NONTEST_PROG_SRC:programs/%.c=%$(PROG_SUFFIX))
 DEFAULT_TARGETS  += $(NONTEST_PROGRAMS)

programs/test_zlib.c

@@ -0,0 +1,106 @@
+/*
+ * test_zlib.c
+ *
+ * Verify that libdeflate_zlib_decompress and libdeflate_zlib_decompress_ex can
+ * correctly decompress the results of libdeflate_zlib_compress.  Also checks
+ * whether decompression correctly handles additional trailing bytes in the
+ * compressed buffer.
+ */
+
+#include <stdlib.h>
+
+#include "test_util.h"
+
+static void
+test_decompress(u8 const* compressed, size_t compressed_nbytes,
+		u8 const* expected, size_t expected_nbytes)
+{
+	struct libdeflate_decompressor* d = libdeflate_alloc_decompressor();
+	ASSERT(d != NULL);
+
+	size_t decompressed_nbytes = expected_nbytes;
+	u8 *decompressed = xmalloc(decompressed_nbytes);
+
+	size_t actual_decompressed_nbytes = 0;
+	enum libdeflate_result res =
+		libdeflate_zlib_decompress(d, compressed, compressed_nbytes,
+					   decompressed, decompressed_nbytes,
+					   &actual_decompressed_nbytes);
+	ASSERT(res == LIBDEFLATE_SUCCESS);
+	ASSERT(actual_decompressed_nbytes == expected_nbytes);
+	ASSERT(memcmp(expected, decompressed, expected_nbytes) == 0);
+
+	free(decompressed);
+	libdeflate_free_decompressor(d);
+}
+
+static void
+test_decompress_ex(u8 const* compressed, size_t compressed_nbytes,
+		   size_t expected_actual_compressed_nbytes,
+		   u8 const* expected, size_t expected_nbytes)
+{
+	struct libdeflate_decompressor* d = libdeflate_alloc_decompressor();
+	ASSERT(d != NULL);
+
+	size_t decompressed_nbytes = expected_nbytes;
+	u8 *decompressed = xmalloc(decompressed_nbytes);
+
+	size_t actual_compressed_nbytes = 0;
+	size_t actual_decompressed_nbytes = 0;
+	enum libdeflate_result res =
+		libdeflate_zlib_decompress_ex(d, compressed, compressed_nbytes,
+					      decompressed, decompressed_nbytes,
+					      &actual_compressed_nbytes,
+					      &actual_decompressed_nbytes);
+	ASSERT(res == LIBDEFLATE_SUCCESS);
+	ASSERT(actual_compressed_nbytes == expected_actual_compressed_nbytes);
+	ASSERT(actual_decompressed_nbytes == expected_nbytes);
+	ASSERT(memcmp(expected, decompressed, expected_nbytes) == 0);
+
+	free(decompressed);
+	libdeflate_free_decompressor(d);
+}
+
+int
+tmain(int argc, tchar *argv[])
+{
+	program_invocation_name = get_filename(argv[0]);
+
+	size_t original_nbytes = 32768;
+	u8 *original = xmalloc(original_nbytes);
+
+	/* Prepare some dummy data to compress */
+	for (size_t i = 0; i < original_nbytes; ++i) {
+		original[i] = (i % 123) + (i % 1023);
+	}
+
+	size_t compressed_nbytes_total = 32768;
+	u8 *compressed = xmalloc(compressed_nbytes_total);
+	memset(compressed, 0x00, compressed_nbytes_total);
+
+	/*
+	 * Don't use the full buffer for compressed data, because we want to
+	 * test whether decompression can deal with additional trailing bytes.
+	 */
+	size_t compressed_nbytes_avail = 30000;
+	ASSERT(compressed_nbytes_avail < compressed_nbytes_total);
+
+	struct libdeflate_compressor* c = libdeflate_alloc_compressor(6);
+	ASSERT(c != NULL);
+	size_t compressed_nbytes =
+		libdeflate_zlib_compress(c, original, original_nbytes,
+					 compressed, compressed_nbytes_avail);
+	ASSERT(compressed_nbytes > 0);
+	libdeflate_free_compressor(c);
+
+	test_decompress(compressed, compressed_nbytes, original, original_nbytes);
+	test_decompress(compressed, compressed_nbytes_total, original, original_nbytes);
+	test_decompress_ex(compressed, compressed_nbytes_total, compressed_nbytes,
+			   original, original_nbytes);
+
+	printf("libdeflate_zlib_* tests passed!\n");
+
+	free(compressed);
+	free(original);
+	return 0;
+}