--- a/include/jeffpc/int.h	Sat Mar 28 10:36:52 2020 -0400
+++ b/include/jeffpc/int.h	Sat Mar 28 10:39:35 2020 -0400
@@ -117,6 +117,33 @@
 	return !(val & (val - 1));
 }
 
+/* round val to the next multiple of power of 2 */
+static inline uint64_t p2roundup(uint64_t val, uint64_t align)
+{
+	if (align <= 1)
+		return val;
+
+	/*
+	 * alignment must be a power of two - if it isn't, panic
+	 *
+	 * Note: We cannot include error.h since we don't want everyone that
+	 * includes in types.h (and therefore int.h) to automatically pull
+	 * in error.h.  We work around it by making a local prototype and
+	 * then calling it.  This is still type safe, since many places
+	 * include both error.h (and therefore get the real panic prototype)
+	 * and this header.  In those compilation units, the compiler makes
+	 * sure that the two signatures match.  No warnings/errors there,
+	 * imply that the below prototype is 100% correct.
+	 */
+	if (!is_p2(align)) {
+		extern void panic(const char *, ...);
+
+		panic("roundup - non-power of 2 align: %#"PRIx64, align);
+	}
+
+	return (val + (align - 1)) & ~(align - 1);
+}
+
 /*
  * These prototypes exist to catch bugs in the code generating macros below.
  */

--- a/tests/.hgignore	Sat Mar 28 10:36:52 2020 -0400
+++ b/tests/.hgignore	Sat Mar 28 10:39:35 2020 -0400
@@ -37,6 +37,7 @@
 test_mutex-unlock-unheld
 test_nvl
 test_nvl_pack
+test_p2roundup
 test_padding
 test_qstring
 test_rwlock-destroy-memcpy

--- a/tests/CMakeLists.txt	Sat Mar 28 10:36:52 2020 -0400
+++ b/tests/CMakeLists.txt	Sat Mar 28 10:39:35 2020 -0400
@@ -66,6 +66,7 @@
 build_test_bin_and_run(mutex-unlock-unheld)
 endif()
 build_test_bin_and_run(nvl)
+build_test_bin_and_run(p2roundup)
 build_test_bin_and_run(padding)
 build_test_bin_and_run(rwlock-destroy-memcpy)
 build_test_bin_and_run(rwlock-destroy-null)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test_p2roundup.c	Sat Mar 28 10:39:35 2020 -0400
@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2020 Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include <jeffpc/types.h>
+
+#include "test.c"
+
+#define CHECK(name, idx, _val, _align, _exp)				\
+	do {								\
+		const uint64_t v = (_val);				\
+		const uint64_t a = (_align);				\
+		const uint64_t exp = (_exp);				\
+		uint64_t got;						\
+									\
+		fprintf(stderr, "%s: %2d: p2roundup(%#018"PRIx64", "	\
+			"%#018"PRIx64")...", (name), (idx), v, a);	\
+									\
+		got = p2roundup(v, a);					\
+		if (got != exp)						\
+			fail("expected %#018"PRIx64", got %#018"PRIx64,	\
+			     exp, got);					\
+									\
+		fprintf(stderr, "ok.\n");				\
+	} while (0)
+
+#define TEST(name, _in, out)						\
+	do {								\
+		const uint64_t val = (_in);				\
+		int shift;						\
+									\
+		/* no alignment -> no change */				\
+		CHECK((name), 0, val, 0ul, val);			\
+		CHECK((name), 1, val, 1ul, val);			\
+									\
+		for (shift = 1; shift < 64; shift++) {			\
+			const uint64_t align = 1ull << shift;		\
+			CHECK((name), shift + 1, val, align, (out));	\
+		}							\
+	} while (0)
+
+void test(void)
+{
+	/* aligning zero always yields zero */
+	TEST("zero", 0ul, 0);
+
+	/* aligning one always yields alignment */
+	TEST("one", 1ul, align);
+
+	/* aligning INT64_MAX yields INT64_MAX+1 */
+	TEST("INT64_MAX", INT64_MAX, ((uint64_t) INT64_MAX) + 1);
+
+	/* aligning UINT64_MAX yields zero because of overflow */
+	TEST("UINT64_MAX", UINT64_MAX, 0);
+
+	/* check against alternate implementations */
+#define TEST_BATCH(name) \
+	do { \
+		TEST(name " 0x111...", 0x1111111111111111, ALT_IMPL); \
+		TEST(name " 0x555...", 0x5555555555555555, ALT_IMPL); \
+		TEST(name " 0xaaa...", 0xaaaaaaaaaaaaaaaa, ALT_IMPL); \
+		TEST(name " digits asc", 0x0123456789abcdef, ALT_IMPL); \
+		TEST(name " digits desc", 0xfedcba9876543210, ALT_IMPL); \
+	} while (0)
+
+#define ALT_IMPL (((val >> shift) + ((val << (64 - shift)) ? 1 : 0)) << shift)
+	TEST_BATCH("ALT1");
+#undef ALT_IMPL
+#define ALT_IMPL (val + ((val % align) ? (align - (val % align)) : 0))
+	TEST_BATCH("ALT2");
+#undef ALT_IMPL
+#define ALT_IMPL (val + ((val & (align - 1)) ? (align - (val & (align - 1))) : 0))
+	TEST_BATCH("ALT3");
+#undef ALT_IMPL
+}