path: root/lib/bitmap.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * lib/bitmap.c
 * Helper functions for bitmap.h.
 */

#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/ctype.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/thread_info.h>
#include <linux/uaccess.h>

#include <asm/page.h>

#include "kstrtox.h"

/**
 * DOC: bitmap introduction
 *
 * bitmaps provide an array of bits, implemented using an
 * array of unsigned longs.  The number of valid bits in a
 * given bitmap does _not_ need to be an exact multiple of
 * BITS_PER_LONG.
 *
 * The possible unused bits in the last, partially used word
 * of a bitmap are 'don't care'.  The implementation makes
 * no particular effort to keep them zero.  It ensures that
 * their value will not affect the results of any operation.
 * The bitmap operations that return Boolean (bitmap_empty,
 * for example) or scalar (bitmap_weight, for example) results
 * carefully filter out these unused bits from impacting their
 * results.
 *
 * The byte ordering of bitmaps is more natural on little
 * endian architectures.  See the big-endian headers
 * include/asm-ppc64/bitops.h and include/asm-s390/bitops.h
 * for the best explanations of this ordering.
 */

bool __bitmap_equal(const unsigned long *bitmap1,
		    const unsigned long *bitmap2, unsigned int bits)
{
	unsigned int k, lim = bits/BITS_PER_LONG;
	for (k = 0; k < lim; ++k)
		if (bitmap1[k] != bitmap2[k])
			return false;

	if (bits % BITS_PER_LONG)
		if ((bitmap1[k] ^ bitmap2[k]) & BITMAP_LAST_WORD_MASK(bits))
			return false;

	return true;
}
EXPORT_SYMBOL(__bitmap_equal);

bool __bitmap_or_equal(const unsigned long *bitmap1,
		       const unsigned long *bitmap2,
		       const unsigned long *bitmap3,
		       unsigned int bits)
{
	unsigned int k, lim = bits / BITS_PER_LONG;
	unsigned long tmp;

	for (k = 0; k < lim; ++k) {
		if ((bitmap1[k] | bitmap2[k]) != bitmap3[k])
			return false;
	}

	if (!(bits % BITS_PER_LONG))
		return true;

	tmp = (bitmap1[k] | bitmap2[k]) ^ bitmap3[k];
	return (tmp & BITMAP_LAST_WORD_MASK(bits)) == 0;
}

void __bitmap_complement(unsigned long *dst, const unsigned long *src, unsigned int bits)
{
	unsigned int k, lim = BITS_TO_LONGS(bits);
	for (k = 0; k < lim; ++k)
		dst[k] = ~src[k];
}
EXPORT_SYMBOL(__bitmap_complement);

/**
 * __bitmap_shift_right - logical right shift of the bits in a bitmap
 *   @dst : destination bitmap
 *   @src : source bitmap
 *   @shift : shift by this many bits
 *   @nbits : bitmap size, in bits
 *
 * Shifting right (dividing) means moving bits in the MS -> LS bit
 * direction.  Zeros are fed into the vacated MS positions and the
 * LS bits shifted off the bottom are lost.
 */
void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
			unsigned shift, unsigned nbits)
{
	unsigned k, lim = BITS_TO_LONGS(nbits);
	unsigned off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
	unsigned long mask = BITMAP_LAST_WORD_MASK(nbits);
	for (k = 0; off + k < lim; ++k) {
		unsigned long upper, lower;

		/*
		 * If shift is not word aligned, take lower rem bits of
		 * word above and make them the top rem bits of result.
		 */
		if (!rem || off + k + 1 >= lim)
			upper = 0;
		else {
			upper = src[off + k + 1];
			if (off + k + 1 == lim - 1)
				upper &= mask;
			upper <<= (BITS_PER_LONG - rem);
		}
		lower = src[off + k];
		if (off + k == lim - 1)
			lower &= mask;
		lower >>= rem;
		dst[k] = lower | upper;
	}
	if (off)
		memset(&dst[lim - off], 0, off*sizeof(unsigned long));
}
EXPORT_SYMBOL(__bitmap_shift_right);


/**
 * __bitmap_shift_left - logical left shift of the bits in a bitmap
 *   @dst : destination bitmap
 *   @src : source bitmap
 *   @shift : shift by this many bits
 *   @nbits : bitmap size, in bits
 *
 * Shifting left (multiplying) means moving bits in the LS -> MS
 * direction.  Zeros are fed into the vacated LS bit positions
 * and those MS bits shifted off the top are lost.
 */

void __bitmap_shift_left(unsigned long *dst, const unsigned long *src,
			unsigned int shift, unsigned int nbits)
{
	int k;
	unsigned int lim = BITS_TO_LONGS(nbits);
	unsigned int off = shift/BITS_PER_LONG, rem = shift % BITS_PER_LONG;
	for (k = lim - off - 1; k >= 0; --k) {
		unsigned long upper, lower;

		/*
		 * If shift is not word aligned, take upper rem bits of
		 * word below and make them the bottom rem bits of result.
		 */
		if (rem && k > 0)
			lower = src[k - 1] >> (BITS_PER_LONG - rem);
		else
			lower = 0;
		upper = src[k] << rem;
		dst[k + off] = lower | upper;
	}
	if (off)
		memset(dst, 0, off*sizeof(unsigned long));
}
EXPORT_SYMBOL(__bitmap_shift_left);

/**
 * bitmap_cut() - remove bit region from bitmap and right shift remaining bits
 * @dst: destination bitmap, might overlap with src
 * @src: source bitmap
 * @first: start bit of region to be removed
 * @cut: number of bits to remove
 * @nbits: bitmap size, in bits
 *
 * Set the n-th bit of @dst iff the n-th bit of @src is set and
 * n is less than @first, or the m-th bit of @src is set for any
 * m such that @first <= n < nbits, and m = n + @cut.
 *
 * In pictures, example for a big-endian 32-bit architecture:
 *
 * The @src bitmap is::
 *
 *   31                                   63
 *   |                                    |
 *   10000000 11000001 11110010 00010101  10000000 11000001 01110010 00010101
 *                   |  |              |                                    |
 *                  16  14             0                                   32
 *
 * if @cut is 3, and @first is 14, bits 14-16 in @src are cut and @dst is::
 *
 *   31                                   63
 *   |                                    |
 *   10110000 00011000 00110010 00010101  00010000 00011000 00101110 01000010
 *                      |              |                                    |
 *                      14 (bit 17     0                                   32
 *                          from @src)
 *
 * Note that @dst and @src might overlap partially or entirely.
 *
 * This is implemented in the obvious way, with a shift and carry
 * step for each moved bit. Optimisation is left as an exercise
 * for the compiler.
 */
void bitmap_cut(unsigned long *dst, const unsigned long *src,
		unsigned int first, unsigned int cut, unsigned int nbits)
{
	unsigned int len = BITS_TO_LONGS(nbits);
	unsigned long keep = 0, carry;
	int i;

	if (first % BITS_PER_LONG) {
		keep = src[first / BITS_PER_LONG] &
		       (~0UL >> (BITS_PER_LONG - first % BITS_PER_LONG));
	}

	memmove(dst, src, len * sizeof(*dst));

	while (cut--) {
		for (i = first / BITS_PER_LONG; i < len; i++) {
			if (i < len - 1)
				carry = dst[i + 1] & 1UL;
			else
				carry = 0;

			dst[i] = (dst[i] >> 1) | (carry <&