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diff --git a/lib/liboqs/src/sig/sphincs/pqclean_sphincs-shake256-256s-simple_clean/hash_state.h b/lib/liboqs/src/sig/sphincs/pqclean_sphincs-shake256-256s-simple_clean/hash_state.h
new file mode 100644
index 000000000..7d92ef872
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+++ b/lib/liboqs/src/sig/sphincs/pqclean_sphincs-shake256-256s-simple_clean/hash_state.h
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+#ifndef SPX_HASH_STATE_H
+#define SPX_HASH_STATE_H
+
+/**
+ * Defines the type of the hash function state.
+ *
+ * Don't be fooled into thinking this instance of SPHINCS+ isn't stateless!
+ *
+ * From Section 7.2.2 from the SPHINCS+ round-2 specification:
+ *
+ * Each of the instances of the tweakable hash function take PK.seed as its
+ * first input, which is constant for a given key pair – and, thus, across
+ * a single signature. This leads to a lot of redundant computation. To remedy
+ * this, we pad PK.seed to the length of a full 64-byte SHA-256 input block.
+ * Because of the Merkle-Damgård construction that underlies SHA-256, this
+ * allows for reuse of the intermediate SHA-256 state after the initial call to
+ * the compression function which improves performance.
+ *
+ * We pass this hash state around in functions, because otherwise we need to
+ * have a global variable.
+ *
+ * SHAKE256 does not need this state. Because this implementation is generated
+ * from a shared code base, we still need to specify some hash_state as it is
+ * still passed around. We chose to use an `int` as a placeholder for this
+ * purpose.
+ */
+
+#define hash_state int
+
+#endif