sort telephone number

sortnumber.c

#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <stdio.h>

#define N (100000063/64)

struct bitset {
	uint64_t bits[N];
};

static struct bitset *
number_new() {
	struct bitset *S = (struct bitset *)malloc(sizeof(*S));
	memset(S, 0, sizeof(*S));
	return S;
}

static void
number_delete(struct bitset *S) {
	if (S)
		free(S);
}

static void
number_insert(struct bitset *S, uint32_t v) {
	assert(v < N * 64);
	S->bits[v / 64] |= 1 << (v % 64);
}

static void
number_writefile(const char * filename, struct bitset *S) {
	FILE *f = fopen(filename, "wb");
	if (f == NULL)
		return;
	int i,j;
	for (i=0;i<N;i++) {
		uint64_t v = S->bits[i];
		for (j = 0; j < 64 && v != 0; j++) {
			if (v & 1) {
				fprintf(f, "%d\n", i * 64 + j);
			}
			v >>= 1;
		}
	}
	fclose(f);
}

static void
number_readfile(const char * filename, struct bitset *S) {
	FILE *f = fopen(filename, "rb");
	char line[1024];
	for (;;) {
		char * s = fgets(line, sizeof(line), f);
		if (s == NULL)
			return;
		uint32_t v;
		if (sscanf(s, "%d", &v) == 1) {
			number_insert(S, v);
		}
	}
}

#ifdef TEST_MAIN

int
main() {
	struct bitset *S = number_new();
	printf("READ\n");
	number_readfile("number.txt", S);
	printf("WRITE\n");
	number_writefile("sorted.txt", S);
	number_delete(S);
	return 0;
}

#endif

#ifdef GEN_TEST_NUMBER

#include <stdlib.h>

#define N 80000000

int
main() {
	FILE *f = fopen("number.txt", "w");
	if (f == NULL)
		return 1;
	int i;
	for (i=0;i<N;i++) {
		uint16_t a = rand() % 10000;
		uint16_t b = rand() % 10000;
		uint32_t n = (a * 10000 + b ) % 89999999 + 10000000;
		fprintf(f, "%d\n", n);
	}

	fclose(f);
	return 0;
}

#endif

Hi, 大佬您好，想问您一下为什么用 #define N (100000063/64) 而不是直接使用 100000000/64 计算，是有什么通用的考虑嘛？