手搓位图bitmap

bitmap.h

#pragma once
#include<stdbool.h>
#include<stdint.h>
#include<stdlib.h>

typedef uint32_t Word;

typedef struct {
	Word* array;
	size_t bits;
}BitMap;

BitMap* bitmap_create(size_t bits);
void bitmap_destory(BitMap* bm);

void bitmap_set(BitMap* bm, size_t n);
void bitmap_unset(BitMap* bm, size_t n);
bool bitmap_isset(BitMap* bm, size_t n);
void bitmap_clear(BitMap* bm);

bitmap.c

#include"bitmap.h"
#include<stdlib.h>
#include<string.h>
#include<stdio.h>
#define BITS_PER_WORD 32
#define BITMAP_SHIFT 5
#define BITMAP_MASK 0x1F
//存储bits位，需要多少个word
#define BITMAP_SIZE(bits) ((bits+ BITS_PER_WORD -1) >> BITMAP_SHIFT)

BitMap* bitmap_create(size_t bits) {
	BitMap* bm = malloc(sizeof(BitMap));

	bm->array = calloc(BITMAP_SIZE(bits), sizeof(Word));
	bm->bits = bits;

	return bm;
}


void grow_capacity(BitMap* bm, size_t bits) {
	Word* new_array = realloc(bm->array, BITMAP_SIZE(bits) * sizeof(Word));
	if (new_array == NULL) {
		printf("ERROR:relloc failed in grow_capacity\n");
		exit(1);
	}
	bm->array = new_array;
	int bytes = (BITMAP_SIZE(bits) - BITMAP_SIZE(bm->bits)) * sizeof(Word);
	memset(bm->array + BITMAP_SIZE(bm->bits), 0, bytes);
}

void bitmap_set(BitMap* bm, size_t n) {
	if (n >= bm->bits) {
		if (BITMAP_SIZE(n + 1) > BITMAP_SIZE(bm->bits)) {
			grow_capacity(bm, n + 1);
		}
		bm->bits = n + 1;

	}
	size_t word = n >> BITMAP_SHIFT;
	size_t offset = n & BITMAP_MASK;
	bm->array[word] |= (0x1 << offset);

}

void bitmap_unset(BitMap* bm, size_t n) {
	size_t word = n >> BITMAP_SHIFT;
	size_t offset = n & BITMAP_MASK;
	bm->array[word] &= ~(0x1 << offset);
}

bool bitmap_isset(BitMap* bm, size_t n ) {
	size_t word = n >> BITMAP_SHIFT;
	size_t offset = n & BITMAP_MASK;
	return bm->array[word] & (0x1 << offset);
}

void bitmap_clear(BitMap* bm) {
	size_t bytes = BITMAP_SIZE(bm->bits) * sizeof(Word);
	memset(bm->array, 0, bytes);
}

void bitmap_destory(BitMap* bm) {
	free(bm->array);
	free(bm);
}

应用场景，排序，去重，面试：用一个数据结构存储qq在线人数-》bitmap。

特点：内存紧凑。