CRC32源码

CRC32源码

C语言版

static u32 CRC32[256];
static bool init = 0;

//初始化表,在单片机等RAM较小的系统,可以在源码中把tab构造为const数组
static void init_table() {
   for (int i = 0; i < 256; i++) {
      u32 crc = i;
      for (int j = 0; j < 8; j++) {
         if (crc & 1) {
            crc = (crc >> 1) ^ 0xEDB88320;
         }
         else {
            crc = crc >> 1;
         }
      }
      CRC32[i] = crc;
   }
}

//crc32实现函数
u32 crc32(const u8* buf, int len) {
   u32 ret = 0xFFFFFFFF;
   if (!init) {
      init_table();
      init = true;
   }
   for (int i = 0; i < len; i++) {
      ret = CRC32[((ret & 0xFF) ^ buf[i])] ^ (ret >> 8);
   }
   ret = ~ret;
   return ret;
}

纯JAVA版

/**
 * 纯java实现的CRC32
 * @author houj
 *
 */
public class Crc32 {
   static int[] CRC32 = new int[256];
   static boolean init = false;

   /**
    * 初始化表
    */
   static void init_table() {
      for (int i = 0; i < 256; i++) {
         int crc = i;
         for (int j = 0; j < 8; j++) {
            if ((crc & 1) != 0) {
               crc = (crc >>> 1) ^ 0xEDB88320;
            } else {
               crc = crc >>> 1;
            }
         }
         CRC32[i] = crc;
      }
   }

   /**
    * crc32实现函数
    * 
    * @param buf
    * @param len
    * @return
    */
   public static int crc32(byte[] buf, int len) {
      int ret = 0xFFFFFFFF;
      int i;
      if (!init) {
         init_table();
         init = true;
      }
      for (i = 0; i < len; i++) {
         ret = CRC32[(((ret & 0xFF) ^ buf[i])) & 0xFF] ^ (ret >>> 8);
      }
      ret = ~ret;
      return ret;
   }

   /**
    * 测试
    * 
    * @param args
    */
   public static void main(String[] args) {
      // 构造数据
      byte[] bs = new byte[4096];
      new java.util.Random().nextBytes(bs);
      
      //纯java实现
      int r = crc32(bs, bs.length);
      System.out.println(r);

      //java原生实现
      java.util.zip.CRC32 c3 = new java.util.zip.CRC32();
      c3.reset();
      c3.update(bs, 0, bs.length);
      int r2 = (int) c3.getValue();
      System.out.println(r2);
      
      System.out.println("OK:"+(r==r2));
   }
}

转载于:https://my.oschina.net/u/184090/blog/338558