lib: linux: Add find_bit from Linux

Add lib/find_bit.c and include/linux/find.h from Linux v6.19, trimmed
to include only the functions needed for ext4l: find_first_bit(),
find_first_zero_bit(), find_next_bit(), find_next_zero_bit() and
find_last_bit()

The following items are removed from the Linux originals:
- find.h: _and_bit, _andnot_bit, _or_bit, _nth_bit variants, wrap
  functions, clump8 functions, big-endian support, most for_each_...
  macros
- find_bit.c: Corresponding implementations, random.h include

Add wrapper functions matching sandbox's asm/bitops.h declarations
(int return type, void* addr) that call the _find_* implementations.

Build find_bit.o only for sandbox for now.

Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

include/linux/find.h

@@ -0,0 +1,176 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_FIND_H_
+#define __LINUX_FIND_H_
+
+#include <linux/bitops.h>
+
+unsigned long _find_next_bit(const unsigned long *addr1, unsigned long nbits,
+				unsigned long start);
+unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
+					 unsigned long start);
+extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
+extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
+extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);
+
+#ifndef find_next_bit
+/**
+ * find_next_bit - find the next set bit in a memory region
+ * @addr: The address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+static __always_inline
+unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
+			    unsigned long offset)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr & GENMASK(size - 1, offset);
+		return val ? __ffs(val) : size;
+	}
+
+	return _find_next_bit(addr, size, offset);
+}
+#endif
+
+#ifndef find_next_zero_bit
+/**
+ * find_next_zero_bit - find the next cleared bit in a memory region
+ * @addr: The address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number of the next zero bit
+ * If no bits are zero, returns @size.
+ */
+static __always_inline
+unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
+				 unsigned long offset)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr | ~GENMASK(size - 1, offset);
+		return val == ~0UL ? size : ffz(val);
+	}
+
+	return _find_next_zero_bit(addr, size, offset);
+}
+#endif
+
+#ifndef find_first_bit
+/**
+ * find_first_bit - find the first set bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The maximum number of bits to search
+ *
+ * Returns the bit number of the first set bit.
+ * If no bits are set, returns @size.
+ */
+static __always_inline
+unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val = *addr & GENMASK(size - 1, 0);
+
+		return val ? __ffs(val) : size;
+	}
+
+	return _find_first_bit(addr, size);
+}
+#endif
+
+#ifndef find_first_zero_bit
+/**
+ * find_first_zero_bit - find the first cleared bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The maximum number of bits to search
+ *
+ * Returns the bit number of the first cleared bit.
+ * If no bits are zero, returns @size.
+ */
+static __always_inline
+unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val = *addr | ~GENMASK(size - 1, 0);
+
+		return val == ~0UL ? size : ffz(val);
+	}
+
+	return _find_first_zero_bit(addr, size);
+}
+#endif
+
+#ifndef find_last_bit
+/**
+ * find_last_bit - find the last set bit in a memory region
+ * @addr: The address to start the search at
+ * @size: The number of bits to search
+ *
+ * Returns the bit number of the last set bit, or size.
+ */
+static __always_inline
+unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val = *addr & GENMASK(size - 1, 0);
+
+		return val ? __fls(val) : size;
+	}
+
+	return _find_last_bit(addr, size);
+}
+#endif
+
+#if defined(__LITTLE_ENDIAN)
+
+static __always_inline
+unsigned long find_next_zero_bit_le(const void *addr, unsigned long size, unsigned long offset)
+{
+	return find_next_zero_bit(addr, size, offset);
+}
+
+static __always_inline
+unsigned long find_next_bit_le(const void *addr, unsigned long size, unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+
+static __always_inline
+unsigned long find_first_zero_bit_le(const void *addr, unsigned long size)
+{
+	return find_first_zero_bit(addr, size);
+}
+
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+
+#define for_each_set_bit(bit, addr, size) \
+	for ((bit) = 0; (bit) = find_next_bit((addr), (size), (bit)), (bit) < (size); (bit)++)
+
+/* same as for_each_set_bit() but use bit as value to start with */
+#define for_each_set_bit_from(bit, addr, size) \
+	for (; (bit) = find_next_bit((addr), (size), (bit)), (bit) < (size); (bit)++)
+
+#define for_each_clear_bit(bit, addr, size) \
+	for ((bit) = 0;									\
+	     (bit) = find_next_zero_bit((addr), (size), (bit)), (bit) < (size);		\
+	     (bit)++)
+
+/* same as for_each_clear_bit() but use bit as value to start with */
+#define for_each_clear_bit_from(bit, addr, size) \
+	for (; (bit) = find_next_zero_bit((addr), (size), (bit)), (bit) < (size); (bit)++)
+
+#endif /*__LINUX_FIND_H_ */

lib/Makefile

@@ -58,6 +58,7 @@ obj-$(CONFIG_PHYSMEM) += physmem.o
 obj-y += rc4.o
 obj-$(CONFIG_RBTREE)	+= rbtree.o
 obj-$(CONFIG_BITREVERSE) += bitrev.o
+obj-$(CONFIG_SANDBOX) += find_bit.o
 obj-y += list_sort.o
 endif
 

lib/find_bit.c

@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* bit search implementation
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * Copyright (C) 2008 IBM Corporation
+ * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
+ * (Inspired by David Howell's find_next_bit implementation)
+ *
+ * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
+ * size and improve performance, 2015.
+ */
+
+#include <asm/byteorder.h>
+#include <linux/bitops.h>
+#include <linux/bitmap.h>
+#include <linux/export.h>
+
+/*
+ * Common helper for find_bit() function family
+ * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
+ * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
+ * @size: The bitmap size in bits
+ */
+#define FIND_FIRST_BIT(FETCH, MUNGE, size)					\
+({										\
+	unsigned long idx, val, sz = (size);					\
+										\
+	for (idx = 0; idx * BITS_PER_LONG < sz; idx++) {			\
+		val = (FETCH);							\
+		if (val) {							\
+			sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(val)), sz);	\
+			break;							\
+		}								\
+	}									\
+										\
+	sz;									\
+})
+
+/*
+ * Common helper for find_next_bit() function family
+ * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
+ * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
+ * @size: The bitmap size in bits
+ * @start: The bitnumber to start searching at
+ */
+#define FIND_NEXT_BIT(FETCH, MUNGE, size, start)				\
+({										\
+	unsigned long mask, idx, tmp, sz = (size), __start = (start);		\
+										\
+	if (unlikely(__start >= sz))						\
+		goto out;							\
+										\
+	mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start));				\
+	idx = __start / BITS_PER_LONG;						\
+										\
+	for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) {			\
+		if ((idx + 1) * BITS_PER_LONG >= sz)				\
+			goto out;						\
+		idx++;								\
+	}									\
+										\
+	sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz);			\
+out:										\
+	sz;									\
+})
+
+#ifndef find_first_bit
+/*
+ * Find the first set bit in a memory region.
+ */
+unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	return FIND_FIRST_BIT(addr[idx], /* nop */, size);
+}
+EXPORT_SYMBOL(_find_first_bit);
+#endif
+
+#ifndef find_first_zero_bit
+/*
+ * Find the first cleared bit in a memory region.
+ */
+unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size)
+{
+	return FIND_FIRST_BIT(~addr[idx], /* nop */, size);
+}
+EXPORT_SYMBOL(_find_first_zero_bit);
+#endif
+
+#ifndef find_next_bit
+unsigned long _find_next_bit(const unsigned long *addr, unsigned long nbits, unsigned long start)
+{
+	return FIND_NEXT_BIT(addr[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_bit);
+#endif
+
+#ifndef find_next_zero_bit
+unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
+					 unsigned long start)
+{
+	return FIND_NEXT_BIT(~addr[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_zero_bit);
+#endif
+
+#ifndef find_last_bit
+unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
+{
+	if (size) {
+		unsigned long val = BITMAP_LAST_WORD_MASK(size);
+		unsigned long idx = (size-1) / BITS_PER_LONG;
+
+		do {
+			val &= addr[idx];
+			if (val)
+				return idx * BITS_PER_LONG + __fls(val);
+
+			val = ~0ul;
+		} while (idx--);
+	}
+	return size;
+}
+EXPORT_SYMBOL(_find_last_bit);
+#endif
+
+/*
+ * Wrapper functions matching sandbox's asm/bitops.h declarations.
+ * These provide the expected function signatures for sandbox platform.
+ */
+int find_first_zero_bit(void *addr, unsigned int size)
+{
+	return _find_first_zero_bit(addr, size);
+}
+EXPORT_SYMBOL(find_first_zero_bit);
+
+int find_next_zero_bit(void *addr, int size, int offset)
+{
+	return _find_next_zero_bit(addr, size, offset);
+}
+EXPORT_SYMBOL(find_next_zero_bit);