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diff --git a/lib/count-leading-zeros.h b/lib/count-leading-zeros.h
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+/* count-leading-zeros.h -- counts the number of leading 0 bits in a word.
+ Copyright (C) 2012-2022 Free Software Foundation, Inc.
+
+ This file is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as
+ published by the Free Software Foundation; either version 2.1 of the
+ License, or (at your option) any later version.
+
+ This file is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* Written by Eric Blake. */
+
+#ifndef COUNT_LEADING_ZEROS_H
+#define COUNT_LEADING_ZEROS_H 1
+
+#include <limits.h>
+#include <stdlib.h>
+
+#ifndef _GL_INLINE_HEADER_BEGIN
+ #error "Please include config.h first."
+#endif
+_GL_INLINE_HEADER_BEGIN
+#ifndef COUNT_LEADING_ZEROS_INLINE
+# define COUNT_LEADING_ZEROS_INLINE _GL_INLINE
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN,
+ expand to code that computes the number of leading zeros of the local
+ variable 'x' of type TYPE (an unsigned integer type) and return it
+ from the current function. */
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) \
+ || (__clang_major__ >= 4)
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
+ return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
+#elif _MSC_VER
+# pragma intrinsic _BitScanReverse
+# pragma intrinsic _BitScanReverse64
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
+ do \
+ { \
+ unsigned long result; \
+ return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \
+ } \
+ while (0)
+#else
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
+ do \
+ { \
+ int count; \
+ unsigned int leading_32; \
+ if (! x) \
+ return CHAR_BIT * sizeof x; \
+ for (count = 0; \
+ (leading_32 = ((x >> (sizeof (TYPE) * CHAR_BIT - 32)) \
+ & 0xffffffffU), \
+ count < CHAR_BIT * sizeof x - 32 && !leading_32); \
+ count += 32) \
+ x = x << 31 << 1; \
+ return count + count_leading_zeros_32 (leading_32); \
+ } \
+ while (0)
+
+/* Compute and return the number of leading zeros in X,
+ where 0 < X < 2**32. */
+COUNT_LEADING_ZEROS_INLINE int
+count_leading_zeros_32 (unsigned int x)
+{
+ /* <https://github.com/gibsjose/BitHacks>
+ <https://www.fit.vutbr.cz/~ibarina/pub/bithacks.pdf> */
+ static const char de_Bruijn_lookup[32] = {
+ 31, 22, 30, 21, 18, 10, 29, 2, 20, 17, 15, 13, 9, 6, 28, 1,
+ 23, 19, 11, 3, 16, 14, 7, 24, 12, 4, 8, 25, 5, 26, 27, 0
+ };
+
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ return de_Bruijn_lookup[((x * 0x07c4acddU) & 0xffffffffU) >> 27];
+}
+#endif
+
+/* Compute and return the number of leading zeros in X. */
+COUNT_LEADING_ZEROS_INLINE int
+count_leading_zeros (unsigned int x)
+{
+ COUNT_LEADING_ZEROS (__builtin_clz, _BitScanReverse, unsigned int);
+}
+
+/* Compute and return the number of leading zeros in X. */
+COUNT_LEADING_ZEROS_INLINE int
+count_leading_zeros_l (unsigned long int x)
+{
+ COUNT_LEADING_ZEROS (__builtin_clzl, _BitScanReverse, unsigned long int);
+}
+
+/* Compute and return the number of leading zeros in X. */
+COUNT_LEADING_ZEROS_INLINE int
+count_leading_zeros_ll (unsigned long long int x)
+{
+ COUNT_LEADING_ZEROS (__builtin_clzll, _BitScanReverse64,
+ unsigned long long int);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+_GL_INLINE_HEADER_END
+
+#endif /* COUNT_LEADING_ZEROS_H */