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diff --git a/src/lib/intmath/cmp.h b/src/lib/intmath/cmp.h
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+++ b/src/lib/intmath/cmp.h
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+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file cmp.h
+ *
+ * \brief Macro definitions for MIN, MAX, and CLAMP.
+ **/
+
+#ifndef TOR_INTMATH_CMP_H
+#define TOR_INTMATH_CMP_H
+
+/** Macros for MIN/MAX.  Never use these when the arguments could have
+ * side-effects.
+ * {With GCC extensions we could probably define a safer MIN/MAX.  But
+ * depending on that safety would be dangerous, since not every platform
+ * has it.}
+ **/
+#ifndef MAX
+#define MAX(a,b) ( ((a)<(b)) ? (b) : (a) )
+#endif
+#ifndef MIN
+#define MIN(a,b) ( ((a)>(b)) ? (b) : (a) )
+#endif
+
+/* Return <b>v</b> if it's between <b>min</b> and <b>max</b>.  Otherwise
+ * return <b>min</b> if <b>v</b> is smaller than <b>min</b>, or <b>max</b> if
+ * <b>b</b> is larger than <b>max</b>.
+ *
+ * Requires that <b>min</b> is no more than <b>max</b>. May evaluate any of
+ * its arguments more than once! */
+#define CLAMP(min,v,max)                        \
+  ( ((v) < (min)) ? (min) :                     \
+    ((v) > (max)) ? (max) :                     \
+    (v) )
+
+#endif /* !defined(TOR_INTMATH_CMP_H) */