diff --git a/inc/hf/bits.h b/inc/hf/bits.h
new file mode 100644
index 0000000..9b29979
--- /dev/null
+++ b/inc/hf/bits.h
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2024 The Hafnium Authors.
+ *
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/BSD-3-Clause.
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#if defined(__ASSEMBLY__)
+#define STATIC_ASSERT(expr, msg) 0
+#else
+#define STATIC_ASSERT(expr, msg)          \
+	__extension__({                   \
+		static_assert(expr, msg); \
+		0;                        \
+	})
+#endif
+
+/**
+ * NOTE: The below macroos use the notation `[hi:lo]` to mean the bits
+ * from `lo` up-to and including `hi`. This matches the notation used in the
+ * FF-A specification.
+ * Examples:
+ * - bits `[4:0]` of `0xAF` are `1111`,
+ * - bits `[7:4]` of `0xAF` are `1010`,
+ * - bits `[31:0]`  means the lower half of a 64-bit integer
+ * - bits `[63:32]` means the upper half of a 64-bit integer
+ * - bits `[63:0]`  means the whole 64-bit integer
+ */
+
+/**
+ * Isolate the `n`th bit of `value`.
+ */
+#define GET_BIT(value, n)                             \
+	(STATIC_ASSERT((n) < 64, "n out of bounds") + \
+	 ((value) & (UINT64_C(1) << (n))))
+
+/**
+ * Return true if the `n`th bit of `value` is 1.
+ */
+#define IS_BIT_SET(value, n) (GET_BIT(value, n) != 0)
+
+/**
+ * Return true if the `n`th bit of `value` is 0.
+ */
+#define IS_BIT_UNSET(value, n) (GET_BIT(value, n) == 0)
+
+/**
+ * Return a mask suitable for isolating bits `[hi:lo]` of a 64-bit
+ * integer.
+ */
+#define GET_BITS_MASK(hi, lo)                              \
+	(STATIC_ASSERT((hi) < 64, "hi out of bounds") +    \
+	 STATIC_ASSERT((hi) >= (lo), "hi must be >= lo") + \
+	 (((~UINT64_C(0)) - (UINT64_C(1) << (lo)) + 1) &   \
+	  (~UINT64_C(0) >> (64 - 1 - (hi)))))
+
+/**
+ * Isolate bits `[hi:lo]` of `value`.
+ */
+#define GET_BITS(value, hi, lo) ((value)&GET_BITS_MASK(hi, lo))
+
+/**
+ * Return true if any bits `[lo:hi]` of `value` are 1.
+ */
+#define ANY_BITS_SET(value, hi, lo) (GET_BITS(value, hi, lo) != 0)
+
+/**
+ * Return true if all bits `[lo:hi]` of `value` are 1.
+ */
+#define ALL_BITS_SET(value, hi, lo) \
+	(GET_BITS(value, hi, lo) == GET_BITS_MASK(hi, lo))
+
+/**
+ * Return true if any bits `[lo:hi]` of `value` are 0.
+ */
+#define ANY_BITS_UNSET(value, hi, lo) (!ALL_BITS_SET(value, hi, lo))
+
+/**
+ * Return true if all bits `[lo:hi]` of `value` are 0.
+ */
+#define ALL_BITS_UNSET(value, hi, lo) (!ANY_BITS_SET(value, hi, lo))