含16进制的PHP源码解密

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
unsigned long HEX2DEC(const char *s)
{
        int i,t;
        unsigned long sum=0;
        for (i=0; s[i]; i++)
        {
                if ( (s[i]=='0' && s[i+1]=='x') || (s[i]=='\\' && s[i+1]=='x') )
                {    
                      i++;
                      continue; //0xff, \x64, 去前缀
                }
                if ( s[i]>='0' && s[i] <= '9' )
                        t = s[i]-'0';
                else if ( s[i]>='A' && s[i] <= 'F')
                        t = s[i]-'A'+10;
                else if ( s[i]>='a' && s[i]<='f' )
                        t = s[i]-'a'+10;
                else
                        break;
                sum=sum*16+t;
        }
        return sum;
}
int main(void)
{
         FILE *fd = fopen("d:/1.txt", "r");
         fseek(fd,0,SEEK_END);
         unsigned long s = ftell(fd);
         char *p = (char *)malloc(s);
         memset(p, 0, s );
         fseek(fd,0,SEEK_SET);
         fread( p, s, 1, fd);
         fclose(fd);
         // output
         char t[16]={0}, n[2]={0};
         fd = fopen("d:/2.txt", "w+");
         for ( unsigned int i=0; i<strlen(p); i++ )
         {        
              if ( p[i] == '\\' && p[i+1] == 'x' )
              {
                    sprintf(t, "%c%c", p[i+2], p[i+3]);
                    fputc(HEX2DEC(t),fd);
                    i += 3;
                    continue;
              }
              fputc(p[i], fd);
         }
         fclose(fd);
         free(p);
         return 0;
}