/* bitfield.h — fixed-size bitset over uint64 words with hardware popcount.
 *
 * Backs every "set of pieces/blocks" in the engine: a peer's have-set, our own
 * completed pieces, the in-flight request map, interested/choked flags. The
 * count()/find operations use __builtin_popcountll and __builtin_ctzll so a
 * rarest-first picker can scan availability cheaply even for huge torrents.
 */
#ifndef NAUT_BITFIELD_H
#define NAUT_BITFIELD_H

#include "naut/common.h"

typedef struct naut_bitfield {
    uint64_t *words;
    size_t    nbits;
    size_t    nwords;
} naut_bitfield;

naut_err naut_bitfield_init(naut_bitfield *bf, size_t nbits);
void     naut_bitfield_free(naut_bitfield *bf);

NAUT_INLINE bool naut_bitfield_test(const naut_bitfield *bf, size_t i) {
    return (bf->words[i >> 6] >> (i & 63)) & 1u;
}
NAUT_INLINE void naut_bitfield_set(naut_bitfield *bf, size_t i) {
    bf->words[i >> 6] |= (uint64_t)1 << (i & 63);
}
NAUT_INLINE void naut_bitfield_clear(naut_bitfield *bf, size_t i) {
    bf->words[i >> 6] &= ~((uint64_t)1 << (i & 63));
}

void   naut_bitfield_set_all(naut_bitfield *bf);
void   naut_bitfield_clear_all(naut_bitfield *bf);

/* number of set bits */
size_t naut_bitfield_count(const naut_bitfield *bf);
/* true when all nbits bits are set (torrent complete) */
bool   naut_bitfield_all_set(const naut_bitfield *bf);

/* index of first 0 / first 1 bit at or after `from`, or SIZE_MAX if none */
size_t naut_bitfield_find_zero(const naut_bitfield *bf, size_t from);
size_t naut_bitfield_find_set(const naut_bitfield *bf, size_t from);

/* Load/serialize the BEP-3 wire format: MSB-first within each byte. The wire
 * order differs from our little-endian word order, so these are not memcpy. */
void naut_bitfield_from_wire(naut_bitfield *bf, const uint8_t *bytes, size_t nbytes);
void naut_bitfield_to_wire(const naut_bitfield *bf, uint8_t *bytes, size_t nbytes);

#endif /* NAUT_BITFIELD_H */