code综述：找到＆LT; /身体GT;在非空终止字符海峡标签反向搜索 [英] code review: finding </body> tag reverse search on a non-null terminated char str

问题描述

的src 是一个非空终止字符长度的字符串 DATA_LEN 。
我想从这个数组月底开始，并找到 HTML＆LT中第一次出现; / BODY方式＆gt; 标签结果
find_pos 应持＆LT的位置; / BODY＆GT; 与标记的src

是否低于code看起来是正确的你？

 的char * strrcasestr_len（为const char *干草，为size_t haylen，为const char * NDL，为size_t ndllen）
{
   字符* RET = NULL;
   INT I;
   为（ⅰ= haylen  -  ndllen; I＆GT; = 0;我 - ）{
       如果（strncasecmp（安培;！干草[Ⅰ]，NDL，ndllen））{
            打破;
       }
   }
   如果（我== -1）
       返回RET;
   其他
       回报（字符*）及干草[I]
}
 

解决方案

这应该这样做，非常非常快的。

 字符常量* find_body_closing_tag（字符常量* const的SRC，为size_t常量DATA_LEN）
{
    静态字符表[256];
    静态布尔inited;
    如果（！inited）{
         表['＆LT;'] = 1;
         表['/'] = 2;
         表['B'] =表['B'] = 3;
         表['O'] =表['O'] = 4;
         表['D'] =表['D'] = 5;
         表['Y'] =表['Y'] = 6;
         表['＆GT;'] = 7;
         inited = TRUE;
    }    对于（字符常量* P = SRC + DATA_LEN  -  7; P＆GT; = SRC，P  -  = 7）{
        如果（字符偏移量=表[* P]）{
            如果（0 == strnicmp（对 - （偏移1），＆所述; /体＆gt;中，7））返回对 - （偏移1）;
        }
    }
    返回0;
}
 

另外一个非常快速的方法是使用SIMD来测试对 16的连续字符'＆GT; 一次（这是什么 strrchr 或了memrchr 应该是这样做）。

src is a non-null terminated char string whose length is data_len. I want to start from the end of this array, and find the first occurrence of html </body> tag.
find_pos should hold the position of the </body> tag with src

Does the code below look correct to you?

char *strrcasestr_len(const char *hay, size_t haylen, const char *ndl,size_t ndllen)
{    
   char *ret = NULL;
   int i;
   for (i = haylen - ndllen; i >= 0; i--) {
       if (!strncasecmp(&hay[i], ndl, ndllen)) {
            break;
       }
   }
   if (i == -1)
       return ret;
   else
       return (char *)&hay[i];
}

解决方案

This should do it, very very fast.

char const* find_body_closing_tag( char const* const src, size_t const data_len )
{
    static char table[256];
    static bool inited;
    if (!inited) {
         table['<'] = 1;
         table['/'] = 2;
         table['b'] = table['B'] = 3;
         table['o'] = table['O'] = 4;
         table['d'] = table['D'] = 5;
         table['y'] = table['Y'] = 6;
         table['>'] = 7;
         inited = true;
    }

    for( char const* p = src + data_len - 7; p >= src; p -= 7 ) {
        if (char offset = table[*p]) {
            if (0 == strnicmp(p - (offset-1), "</body>", 7)) return p - (offset-1);
        }
    }
    return 0;
}

Another very fast approach would be using SIMD to test 16 consecutive characters against '>' at once (and this is what strrchr or memrchr ought to be doing).

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