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/********************************************
*Created By: Prometheus
*Date : 2009-5-24
********************************************/
/*
* linux/fs/ext2/bitmap.c
*
* Copyright (C) 1992, 1993, 1994 Remy Card (
card@masi.ibp.fr
)
* Laboratoire MASI - Institut Blaise Pascal
* Universite Pierre et Marie Curie (Paris VI)
*/
#include
#include
//这里总共有16个数,他们是0x00-0x0f中0的数目,用半字节为单位来统计空闲的位图
static int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};
unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
{
unsigned int i;
unsigned long sum = 0;
if (!map)
return (0);
for (i = 0; i b_data & 0xf] + //低4比特
nibblemap[(map->b_data >> 4) & 0xf]; //高4比特
return (sum);
}
文档地址:http://blogimg.chinaunix.net/blog/upfile2/090524225100.pdf
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u3/90306/showart_1943495.html |
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