new file mode 100644
--- /dev/null
+++ b/src/core/ngx_crc.h
@@ -0,0 +1,33 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#ifndef _NGX_CRC_H_INCLUDED_
+#define _NGX_CRC_H_INCLUDED_
+
+
+/* 32-bit crc16 */
+
+ngx_inline static uint32_t ngx_crc(char *data, size_t len)
+{
+    uint32_t  sum;
+
+    for (sum = 0; len; len--) {
+
+        /*
+         * gcc 2.95.2 x86 and icc 7.1.006 compile that operator
+         *                                into the single "rol" opcode.
+         * msvc 6.0sp2 compiles it into four opcodes.
+         */
+        sum = sum >> 1 | sum << 31;
+
+        sum += *data++;
+    }
+
+    return sum;
+}
+
+
+#endif /* _NGX_CRC_H_INCLUDED_ */