LwIP udp_input函数校验和代码

最新推荐文章于 2024-11-05 15:13:56 发布

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最新推荐文章于 2024-11-05 15:13:56 发布

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分类专栏： LwIP

本文链接：https://blog.youkuaiyun.com/qq_40943944/article/details/110389815

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本文深入探讨了LwIP网络库中udp_input函数的校验和计算过程，详细解析了如何确保UDP数据包的完整性。通过分析源代码，阐述了校验和的计算原理和关键步骤，帮助读者更好地理解和使用LwIP进行UDP通信。

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#define ip4_addr_get_u32(src_ipaddr) ((src_ipaddr)->addr)
#define FOLD_U32T(u)          (((u) >> 16) + ((u) & 0x0000ffffUL))
#define SWAP_BYTES_IN_WORD(w) (((w) & 0xff) << 8) | (((w) & 0xff00) >> 8)

/*
 * Curt McDowell
 * Broadcom Corp.
 * csm@broadcom.com
 *
 * IP checksum two bytes at a time with support for
 * unaligned buffer.
 * Works for len up to and including 0x20000.
 * by Curt McDowell, Broadcom Corp. 12/08/2005
 *
 * @param dataptr points to start of data to be summed at any boundary
 * @param len length of data to be summed
 * @return host order (!) lwip checksum (non-inverted Internet sum)
 */
u16_t
lwip_standard_chksum(const void *dataptr, int len)
{
   
  const u8_t *pb = (const u8_t *)dataptr;
  const u16_t *ps;
  u16_t t = 0;
  u32_t sum = 0;
  int odd = ((mem_ptr_t)pb & 1);

  /* Get aligned to u16_t */
  if (odd && len > 0) {
   
    ((u8_t *)&t)[1] = *pb++;
    len--;
  }

  /* Add the bulk of the data */
  ps = (const u16_t *)(const void *