jemalloc/src/bitmap.c

#define JEMALLOC_BITMAP_C_
#include "jemalloc/internal/jemalloc_internal.h"

/******************************************************************************/
/* Function prototypes for non-inline static functions. */

static size_t	bits2groups(size_t nbits);

/******************************************************************************/

static size_t
bits2groups(size_t nbits)
{

	return ((nbits >> LG_BITMAP_GROUP_NBITS) +
	    !!(nbits & BITMAP_GROUP_NBITS_MASK));
}

void
bitmap_info_init(bitmap_info_t *binfo, size_t nbits)
{
	unsigned i;
	size_t group_count;

	assert(nbits > 0);
	assert(nbits <= (ZU(1) << LG_BITMAP_MAXBITS));

	/*
	 * Compute the number of groups necessary to store nbits bits, and
	 * progressively work upward through the levels until reaching a level
	 * that requires only one group.
	 */
	binfo->levels[0].group_offset = 0;
	group_count = bits2groups(nbits);
	for (i = 1; group_count > 1; i++) {
		assert(i < BITMAP_MAX_LEVELS);
		binfo->levels[i].group_offset = binfo->levels[i-1].group_offset
		    + group_count;
		group_count = bits2groups(group_count);
	}
	binfo->levels[i].group_offset = binfo->levels[i-1].group_offset
	    + group_count;
	binfo->nlevels = i;
	binfo->nbits = nbits;
}

size_t
bitmap_info_ngroups(const bitmap_info_t *binfo)
{

	return (binfo->levels[binfo->nlevels].group_offset << LG_SIZEOF_BITMAP);
}

size_t
bitmap_size(size_t nbits)
{
	bitmap_info_t binfo;

	bitmap_info_init(&binfo, nbits);
	return (bitmap_info_ngroups(&binfo));
}

void
bitmap_init(bitmap_t *bitmap, const bitmap_info_t *binfo)
{
	size_t extra;
	unsigned i;

	/*
	 * Bits are actually inverted with regard to the external bitmap
	 * interface, so the bitmap starts out with all 1 bits, except for
	 * trailing unused bits (if any).  Note that each group uses bit 0 to
	 * correspond to the first logical bit in the group, so extra bits
	 * are the most significant bits of the last group.
	 */
	memset(bitmap, 0xffU, binfo->levels[binfo->nlevels].group_offset <<
	    LG_SIZEOF_BITMAP);
	extra = (BITMAP_GROUP_NBITS - (binfo->nbits & BITMAP_GROUP_NBITS_MASK))
	    & BITMAP_GROUP_NBITS_MASK;
	if (extra != 0)
		bitmap[binfo->levels[1].group_offset - 1] >>= extra;
	for (i = 1; i < binfo->nlevels; i++) {
		size_t group_count = binfo->levels[i].group_offset -
		    binfo->levels[i-1].group_offset;
		extra = (BITMAP_GROUP_NBITS - (group_count &
		    BITMAP_GROUP_NBITS_MASK)) & BITMAP_GROUP_NBITS_MASK;
		if (extra != 0)
			bitmap[binfo->levels[i+1].group_offset - 1] >>= extra;
	}
}