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authorHarald Welte <laforge@osmocom.org>2020-12-04 21:44:44 +0100
committerHarald Welte <laforge@osmocom.org>2020-12-05 11:39:42 +0100
commit7101ca27516e7ae1db4278bd03ee1a14f9d7fb20 (patch)
tree7aa2134537885807e572cb83a88f4ce01f4b0928
parente3b20edec5684217c0f75d69ac622c4fe7be1480 (diff)
Add hlist and hashtable from Linux kernelHEADmaster
For more than a decade we've used the linuxlist.h for double-linked lists. Let's also add the hlist (double-linked lists with single pointer sized head, and the hashtable that builds on top of it. This reflects the versions included in Linux 5.8 with some modifications to make them build in userspace (remove RCU versions, adjust for userspace include files and types, convert to doxygen). Change-Id: I8ef73a62fe9846ce45058eb21cf999dd3eed5741
-rw-r--r--include/Makefile.am3
-rw-r--r--include/osmocom/core/hash.h101
-rw-r--r--include/osmocom/core/hashtable.h141
-rw-r--r--include/osmocom/core/linuxlist.h247
-rw-r--r--include/osmocom/core/log2.h125
5 files changed, 617 insertions, 0 deletions
diff --git a/include/Makefile.am b/include/Makefile.am
index 71171a48..f13ae76f 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -27,9 +27,12 @@ nobase_include_HEADERS = \
osmocom/core/fsm.h \
osmocom/core/gsmtap.h \
osmocom/core/gsmtap_util.h \
+ osmocom/core/hash.h \
+ osmocom/core/hashtable.h \
osmocom/core/isdnhdlc.h \
osmocom/core/linuxlist.h \
osmocom/core/linuxrbtree.h \
+ osmocom/core/log2.h \
osmocom/core/logging.h \
osmocom/core/loggingrb.h \
osmocom/core/mnl.h \
diff --git a/include/osmocom/core/hash.h b/include/osmocom/core/hash.h
new file mode 100644
index 00000000..b45c0361
--- /dev/null
+++ b/include/osmocom/core/hash.h
@@ -0,0 +1,101 @@
+#pragma once
+#include <osmocom/core/log2.h>
+/* Fast hashing routine for ints, longs and pointers.
+ (C) 2002 Nadia Yvette Chambers, IBM */
+
+#include <limits.h>
+#if ULONG_MAX == 4294967295
+#define BITS_PER_LONG 32
+#else
+#define BITS_PER_LONG 64
+#endif
+
+/*
+ * The "GOLDEN_RATIO_PRIME" is used in ifs/btrfs/brtfs_inode.h and
+ * fs/inode.c. It's not actually prime any more (the previous primes
+ * were actively bad for hashing), but the name remains.
+ */
+#if BITS_PER_LONG == 32
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_32
+#define hash_long(val, bits) hash_32(val, bits)
+#elif BITS_PER_LONG == 64
+#define hash_long(val, bits) hash_64(val, bits)
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_64
+#else
+#error Wordsize not 32 or 64
+#endif
+
+/*
+ * This hash multiplies the input by a large odd number and takes the
+ * high bits. Since multiplication propagates changes to the most
+ * significant end only, it is essential that the high bits of the
+ * product be used for the hash value.
+ *
+ * Chuck Lever verified the effectiveness of this technique:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
+ *
+ * Although a random odd number will do, it turns out that the golden
+ * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
+ * properties. (See Knuth vol 3, section 6.4, exercise 9.)
+ *
+ * These are the negative, (1 - phi) = phi**2 = (3 - sqrt(5))/2,
+ * which is very slightly easier to multiply by and makes no
+ * difference to the hash distribution.
+ */
+#define GOLDEN_RATIO_32 0x61C88647
+#define GOLDEN_RATIO_64 0x61C8864680B583EBull
+
+/*
+ * The _generic versions exist only so lib/test_hash.c can compare
+ * the arch-optimized versions with the generic.
+ *
+ * Note that if you change these, any <asm/hash.h> that aren't updated
+ * to match need to have their HAVE_ARCH_* define values updated so the
+ * self-test will not false-positive.
+ */
+#ifndef HAVE_ARCH__HASH_32
+#define __hash_32 __hash_32_generic
+#endif
+static inline uint32_t __hash_32_generic(uint32_t val)
+{
+ return val * GOLDEN_RATIO_32;
+}
+
+#ifndef HAVE_ARCH_HASH_32
+#define hash_32 hash_32_generic
+#endif
+static inline uint32_t hash_32_generic(uint32_t val, unsigned int bits)
+{
+ /* High bits are more random, so use them. */
+ return __hash_32(val) >> (32 - bits);
+}
+
+#ifndef HAVE_ARCH_HASH_64
+#define hash_64 hash_64_generic
+#endif
+static __always_inline uint32_t hash_64_generic(uint64_t val, unsigned int bits)
+{
+#if BITS_PER_LONG == 64
+ /* 64x64-bit multiply is efficient on all 64-bit processors */
+ return val * GOLDEN_RATIO_64 >> (64 - bits);
+#else
+ /* Hash 64 bits using only 32x32-bit multiply. */
+ return hash_32((uint32_t)val ^ __hash_32(val >> 32), bits);
+#endif
+}
+
+static inline uint32_t hash_ptr(const void *ptr, unsigned int bits)
+{
+ return hash_long((unsigned long)ptr, bits);
+}
+
+/* This really should be called fold32_ptr; it does no hashing to speak of. */
+static inline uint32_t hash32_ptr(const void *ptr)
+{
+ unsigned long val = (unsigned long)ptr;
+
+#if BITS_PER_LONG == 64
+ val ^= (val >> 32);
+#endif
+ return (uint32_t)val;
+}
diff --git a/include/osmocom/core/hashtable.h b/include/osmocom/core/hashtable.h
new file mode 100644
index 00000000..acaf6b91
--- /dev/null
+++ b/include/osmocom/core/hashtable.h
@@ -0,0 +1,141 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Statically sized hash table implementation
+ * (C) 2012 Sasha Levin <levinsasha928@gmail.com>
+ */
+
+#pragma once
+
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/hash.h>
+
+#define DEFINE_HASHTABLE(name, bits) \
+ struct hlist_head name[1 << (bits)] = \
+ { [0 ... ((1 << (bits)) - 1)] = HLIST_HEAD_INIT }
+
+#define DECLARE_HASHTABLE(name, bits) \
+ struct hlist_head name[1 << (bits)]
+
+#define HASH_SIZE(name) (ARRAY_SIZE(name))
+#define HASH_BITS(name) ilog2(HASH_SIZE(name))
+
+/* Use hash_32 when possible to allow for fast 32bit hashing in 64bit kernels. */
+#define hash_min(val, bits) \
+ (sizeof(val) <= 4 ? hash_32(val, bits) : hash_long(val, bits))
+
+static inline void __hash_init(struct hlist_head *ht, unsigned int sz)
+{
+ unsigned int i;
+
+ for (i = 0; i < sz; i++)
+ INIT_HLIST_HEAD(&ht[i]);
+}
+
+/**
+ * hash_init - initialize a hash table
+ * @hashtable: hashtable to be initialized
+ *
+ * Calculates the size of the hashtable from the given parameter, otherwise
+ * same as hash_init_size.
+ *
+ * This has to be a macro since HASH_BITS() will not work on pointers since
+ * it calculates the size during preprocessing.
+ */
+#define hash_init(hashtable) __hash_init(hashtable, HASH_SIZE(hashtable))
+
+/**
+ * hash_add - add an object to a hashtable
+ * @hashtable: hashtable to add to
+ * @node: the &struct hlist_node of the object to be added
+ * @key: the key of the object to be added
+ */
+#define hash_add(hashtable, node, key) \
+ hlist_add_head(node, &hashtable[hash_min(key, HASH_BITS(hashtable))])
+
+/**
+ * hash_hashed - check whether an object is in any hashtable
+ * @node: the &struct hlist_node of the object to be checked
+ */
+static inline bool hash_hashed(struct hlist_node *node)
+{
+ return !hlist_unhashed(node);
+}
+
+static inline bool __hash_empty(struct hlist_head *ht, unsigned int sz)
+{
+ unsigned int i;
+
+ for (i = 0; i < sz; i++)
+ if (!hlist_empty(&ht[i]))
+ return false;
+
+ return true;
+}
+
+/**
+ * hash_empty - check whether a hashtable is empty
+ * @hashtable: hashtable to check
+ *
+ * This has to be a macro since HASH_BITS() will not work on pointers since
+ * it calculates the size during preprocessing.
+ */
+#define hash_empty(hashtable) __hash_empty(hashtable, HASH_SIZE(hashtable))
+
+/**
+ * hash_del - remove an object from a hashtable
+ * @node: &struct hlist_node of the object to remove
+ */
+static inline void hash_del(struct hlist_node *node)
+{
+ hlist_del_init(node);
+}
+
+/**
+ * hash_for_each - iterate over a hashtable
+ * @name: hashtable to iterate
+ * @bkt: integer to use as bucket loop cursor
+ * @obj: the type * to use as a loop cursor for each entry
+ * @member: the name of the hlist_node within the struct
+ */
+#define hash_for_each(name, bkt, obj, member) \
+ for ((bkt) = 0, obj = NULL; obj == NULL && (bkt) < HASH_SIZE(name);\
+ (bkt)++)\
+ hlist_for_each_entry(obj, &name[bkt], member)
+
+/**
+ * hash_for_each_safe - iterate over a hashtable safe against removal of
+ * hash entry
+ * @name: hashtable to iterate
+ * @bkt: integer to use as bucket loop cursor
+ * @tmp: a &struct hlist_node used for temporary storage
+ * @obj: the type * to use as a loop cursor for each entry
+ * @member: the name of the hlist_node within the struct
+ */
+#define hash_for_each_safe(name, bkt, tmp, obj, member) \
+ for ((bkt) = 0, obj = NULL; obj == NULL && (bkt) < HASH_SIZE(name);\
+ (bkt)++)\
+ hlist_for_each_entry_safe(obj, tmp, &name[bkt], member)
+
+/**
+ * hash_for_each_possible - iterate over all possible objects hashing to the
+ * same bucket
+ * @name: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @member: the name of the hlist_node within the struct
+ * @key: the key of the objects to iterate over
+ */
+#define hash_for_each_possible(name, obj, member, key) \
+ hlist_for_each_entry(obj, &name[hash_min(key, HASH_BITS(name))], member)
+
+/**
+ * hash_for_each_possible_safe - iterate over all possible objects hashing to the
+ * same bucket safe against removals
+ * @name: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @tmp: a &struct hlist_node used for temporary storage
+ * @member: the name of the hlist_node within the struct
+ * @key: the key of the objects to iterate over
+ */
+#define hash_for_each_possible_safe(name, obj, tmp, member, key) \
+ hlist_for_each_entry_safe(obj, tmp,\
+ &name[hash_min(key, HASH_BITS(name))], member)
diff --git a/include/osmocom/core/linuxlist.h b/include/osmocom/core/linuxlist.h
index 867605e5..2c3a0a4c 100644
--- a/include/osmocom/core/linuxlist.h
+++ b/include/osmocom/core/linuxlist.h
@@ -16,6 +16,7 @@
* \file linuxlist.h */
#include <stddef.h>
+#include <stdbool.h>
#ifndef inline
#define inline __inline__
@@ -393,6 +394,252 @@ static inline unsigned int llist_count(const struct llist_head *head)
return i;
}
+
+
+/*! Double linked lists with a single pointer list head.
+ * Mostly useful for hash tables where the two pointer list head is
+ * too wasteful.
+ * You lose the ability to access the tail in O(1).
+ */
+
+struct hlist_head {
+ struct hlist_node *first;
+};
+
+struct hlist_node {
+ struct hlist_node *next, **pprev;
+};
+
+#define HLIST_HEAD_INIT { .first = NULL }
+#define HLIST_HEAD(name) struct hlist_head name = { .first = NULL }
+#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)
+static inline void INIT_HLIST_NODE(struct hlist_node *h)
+{
+ h->next = NULL;
+ h->pprev = NULL;
+}
+
+#define READ_ONCE(x) x
+#define WRITE_ONCE(a, b) a = b
+
+/*! Has node been removed from list and reinitialized?.
+ * \param[in] h: Node to be checked
+ * \return 1 if node is unhashed; 0 if not
+ *
+ * Not that not all removal functions will leave a node in unhashed
+ * state. For example, hlist_nulls_del_init_rcu() does leave the
+ * node in unhashed state, but hlist_nulls_del() does not.
+ */
+static inline int hlist_unhashed(const struct hlist_node *h)
+{
+ return !h->pprev;
+}
+
+/*! Version of hlist_unhashed for lockless use.
+ * \param[in] n Node to be checked
+ * \return 1 if node is unhashed; 0 if not
+ *
+ * This variant of hlist_unhashed() must be used in lockless contexts
+ * to avoid potential load-tearing. The READ_ONCE() is paired with the
+ * various WRITE_ONCE() in hlist helpers that are defined below.
+ */
+static inline int hlist_unhashed_lockless(const struct hlist_node *h)
+{
+ return !READ_ONCE(h->pprev);
+}
+
+/*!Is the specified hlist_head structure an empty hlist?.
+ * \param[in] h Structure to check.
+ * \return 1 if hlist is empty; 0 if not
+ */
+static inline int hlist_empty(const struct hlist_head *h)
+{
+ return !READ_ONCE(h->first);
+}
+
+static inline void __hlist_del(struct hlist_node *n)
+{
+ struct hlist_node *next = n->next;
+ struct hlist_node **pprev = n->pprev;
+
+ WRITE_ONCE(*pprev, next);
+ if (next)
+ WRITE_ONCE(next->pprev, pprev);
+}
+
+/*! Delete the specified hlist_node from its list.
+ * \param[in] n: Node to delete.
+ *
+ * Note that this function leaves the node in hashed state. Use
+ * hlist_del_init() or similar instead to unhash @n.
+ */
+static inline void hlist_del(struct hlist_node *n)
+{
+ __hlist_del(n);
+ n->next = LLIST_POISON1;
+ n->pprev = LLIST_POISON2;
+}
+
+/*! Delete the specified hlist_node from its list and initialize.
+ * \param[in] n Node to delete.
+ *
+ * Note that this function leaves the node in unhashed state.
+ */
+static inline void hlist_del_init(struct hlist_node *n)
+{
+ if (!hlist_unhashed(n)) {
+ __hlist_del(n);
+ INIT_HLIST_NODE(n);
+ }
+}
+
+/*! add a new entry at the beginning of the hlist.
+ * \param[in] n new entry to be added
+ * \param[in] h hlist head to add it after
+ *
+ * Insert a new entry after the specified head.
+ * This is good for implementing stacks.
+ */
+static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
+{
+ struct hlist_node *first = h->first;
+ WRITE_ONCE(n->next, first);
+ if (first)
+ WRITE_ONCE(first->pprev, &n->next);
+ WRITE_ONCE(h->first, n);
+ WRITE_ONCE(n->pprev, &h->first);
+}
+
+/*! add a new entry before the one specified.
+ * @n: new entry to be added
+ * @next: hlist node to add it before, which must be non-NULL
+ */
+static inline void hlist_add_before(struct hlist_node *n,
+ struct hlist_node *next)
+{
+ WRITE_ONCE(n->pprev, next->pprev);
+ WRITE_ONCE(n->next, next);
+ WRITE_ONCE(next->pprev, &n->next);
+ WRITE_ONCE(*(n->pprev), n);
+}
+
+/*! add a new entry after the one specified
+ * \param[in] n new entry to be added
+ * \param[in] prev hlist node to add it after, which must be non-NULL
+ */
+static inline void hlist_add_behind(struct hlist_node *n,
+ struct hlist_node *prev)
+{
+ WRITE_ONCE(n->next, prev->next);
+ WRITE_ONCE(prev->next, n);
+ WRITE_ONCE(n->pprev, &prev->next);
+
+ if (n->next)
+ WRITE_ONCE(n->next->pprev, &n->next);
+}
+
+/*! create a fake hlist consisting of a single headless node.
+ * \param[in] n Node to make a fake list out of
+ *
+ * This makes @n appear to be its own predecessor on a headless hlist.
+ * The point of this is to allow things like hlist_del() to work correctly
+ * in cases where there is no list.
+ */
+static inline void hlist_add_fake(struct hlist_node *n)
+{
+ n->pprev = &n->next;
+}
+
+/*! Is this node a fake hlist?.
+ * \param[in] h Node to check for being a self-referential fake hlist.
+ */
+static inline bool hlist_fake(struct hlist_node *h)
+{
+ return h->pprev == &h->next;
+}
+
+/*!is node the only element of the specified hlist?.
+ * \param[in] n Node to check for singularity.
+ * \param[in] h Header for potentially singular list.
+ *
+ * Check whether the node is the only node of the head without
+ * accessing head, thus avoiding unnecessary cache misses.
+ */
+static inline bool
+hlist_is_singular_node(struct hlist_node *n, struct hlist_head *h)
+{
+ return !n->next && n->pprev == &h->first;
+}
+
+/*! Move an hlist.
+ * \param[in] old hlist_head for old list.
+ * \param[in] new hlist_head for new list.
+ *
+ * Move a list from one list head to another. Fixup the pprev
+ * reference of the first entry if it exists.
+ */
+static inline void hlist_move_list(struct hlist_head *old,
+ struct hlist_head *new)
+{
+ new->first = old->first;
+ if (new->first)
+ new->first->pprev = &new->first;
+ old->first = NULL;
+}
+
+#define hlist_entry(ptr, type, member) container_of(ptr,type,member)
+
+#define hlist_for_each(pos, head) \
+ for (pos = (head)->first; pos ; pos = pos->next)
+
+#define hlist_for_each_safe(pos, n, head) \
+ for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
+ pos = n)
+
+#define hlist_entry_safe(ptr, type, member) \
+ ({ typeof(ptr) ____ptr = (ptr); \
+ ____ptr ? hlist_entry(____ptr, type, member) : NULL; \
+ })
+
+/*! iterate over list of given type.
+ * \param[out] pos the type * to use as a loop cursor.
+ * \param[in] head the head for your list.
+ * \param[in] member the name of the hlist_node within the struct.
+ */
+#define hlist_for_each_entry(pos, head, member) \
+ for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member);\
+ pos; \
+ pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+/*! iterate over a hlist continuing after current point.
+ * \param[out] pos the type * to use as a loop cursor.
+ * \param[in] member the name of the hlist_node within the struct.
+ */
+#define hlist_for_each_entry_continue(pos, member) \
+ for (pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member);\
+ pos; \
+ pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+/*! iterate over a hlist continuing from current point.
+ * \param[out] pos the type * to use as a loop cursor.
+ * \param[in] member the name of the hlist_node within the struct.
+ */
+#define hlist_for_each_entry_from(pos, member) \
+ for (; pos; \
+ pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))
+
+/*! hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry.
+ * \param[out] pos the type * to use as a loop cursor.
+ * \param[out] n a &struct hlist_node to use as temporary storage
+ * \param[in] head the head for your list.
+ * \param[in] member the name of the hlist_node within the struct
+ */
+#define hlist_for_each_entry_safe(pos, n, head, member) \
+ for (pos = hlist_entry_safe((head)->first, typeof(*pos), member);\
+ pos && ({ n = pos->member.next; 1; }); \
+ pos = hlist_entry_safe(n, typeof(*pos), member))
+
+
/*!
* @}
*/
diff --git a/include/osmocom/core/log2.h b/include/osmocom/core/log2.h
new file mode 100644
index 00000000..06b20f8c
--- /dev/null
+++ b/include/osmocom/core/log2.h
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Integer base 2 logarithm calculation
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#pragma once
+
+/*
+ * non-constant log of base 2 calculators
+ * - the arch may override these in asm/bitops.h if they can be implemented
+ * more efficiently than using fls() and fls64()
+ * - the arch is not required to handle n==0 if implementing the fallback
+ */
+#ifndef CONFIG_ARCH_HAS_ILOG2_U32
+static inline __attribute__((const))
+int __ilog2_u32(uint32_t n)
+{
+ return fls(n) - 1;
+}
+#endif
+
+#ifndef CONFIG_ARCH_HAS_ILOG2_U64
+static inline __attribute__((const))
+int __ilog2_u64(uint64_t n)
+{
+ return fls64(n) - 1;
+}
+#endif
+
+/**
+ * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
+ * @n: parameter
+ *
+ * Use this where sparse expects a true constant expression, e.g. for array
+ * indices.
+ */
+#define const_ilog2(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ (n) < 2 ? 0 : \
+ (n) & (1ULL << 63) ? 63 : \
+ (n) & (1ULL << 62) ? 62 : \
+ (n) & (1ULL << 61) ? 61 : \
+ (n) & (1ULL << 60) ? 60 : \
+ (n) & (1ULL << 59) ? 59 : \
+ (n) & (1ULL << 58) ? 58 : \
+ (n) & (1ULL << 57) ? 57 : \
+ (n) & (1ULL << 56) ? 56 : \
+ (n) & (1ULL << 55) ? 55 : \
+ (n) & (1ULL << 54) ? 54 : \
+ (n) & (1ULL << 53) ? 53 : \
+ (n) & (1ULL << 52) ? 52 : \
+ (n) & (1ULL << 51) ? 51 : \
+ (n) & (1ULL << 50) ? 50 : \
+ (n) & (1ULL << 49) ? 49 : \
+ (n) & (1ULL << 48) ? 48 : \
+ (n) & (1ULL << 47) ? 47 : \
+ (n) & (1ULL << 46) ? 46 : \
+ (n) & (1ULL << 45) ? 45 : \
+ (n) & (1ULL << 44) ? 44 : \
+ (n) & (1ULL << 43) ? 43 : \
+ (n) & (1ULL << 42) ? 42 : \
+ (n) & (1ULL << 41) ? 41 : \
+ (n) & (1ULL << 40) ? 40 : \
+ (n) & (1ULL << 39) ? 39 : \
+ (n) & (1ULL << 38) ? 38 : \
+ (n) & (1ULL << 37) ? 37 : \
+ (n) & (1ULL << 36) ? 36 : \
+ (n) & (1ULL << 35) ? 35 : \
+ (n) & (1ULL << 34) ? 34 : \
+ (n) & (1ULL << 33) ? 33 : \
+ (n) & (1ULL << 32) ? 32 : \
+ (n) & (1ULL << 31) ? 31 : \
+ (n) & (1ULL << 30) ? 30 : \
+ (n) & (1ULL << 29) ? 29 : \
+ (n) & (1ULL << 28) ? 28 : \
+ (n) & (1ULL << 27) ? 27 : \
+ (n) & (1ULL << 26) ? 26 : \
+ (n) & (1ULL << 25) ? 25 : \
+ (n) & (1ULL << 24) ? 24 : \
+ (n) & (1ULL << 23) ? 23 : \
+ (n) & (1ULL << 22) ? 22 : \
+ (n) & (1ULL << 21) ? 21 : \
+ (n) & (1ULL << 20) ? 20 : \
+ (n) & (1ULL << 19) ? 19 : \
+ (n) & (1ULL << 18) ? 18 : \
+ (n) & (1ULL << 17) ? 17 : \
+ (n) & (1ULL << 16) ? 16 : \
+ (n) & (1ULL << 15) ? 15 : \
+ (n) & (1ULL << 14) ? 14 : \
+ (n) & (1ULL << 13) ? 13 : \
+ (n) & (1ULL << 12) ? 12 : \
+ (n) & (1ULL << 11) ? 11 : \
+ (n) & (1ULL << 10) ? 10 : \
+ (n) & (1ULL << 9) ? 9 : \
+ (n) & (1ULL << 8) ? 8 : \
+ (n) & (1ULL << 7) ? 7 : \
+ (n) & (1ULL << 6) ? 6 : \
+ (n) & (1ULL << 5) ? 5 : \
+ (n) & (1ULL << 4) ? 4 : \
+ (n) & (1ULL << 3) ? 3 : \
+ (n) & (1ULL << 2) ? 2 : \
+ 1) : \
+ -1)
+
+/**
+ * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
+ * @n: parameter
+ *
+ * constant-capable log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ *
+ * selects the appropriately-sized optimised version depending on sizeof(n)
+ */
+#define ilog2(n) \
+( \
+ __builtin_constant_p(n) ? \
+ const_ilog2(n) : \
+ (sizeof(n) <= 4) ? \
+ __ilog2_u32(n) : \
+ __ilog2_u64(n) \
+ )