记录一个自己用CRC效验的场景(分段计算)

是一个项目涉及到固件OTA的场景,在固件在服务器上的数据是固件数据+4字节的固件数据的CRC结果,打包成一个bin,由设备去下载下来然后更新固件.一个固件的大小在100KB左右,MCU用的是比较低端的STM32,RAM想都不用想肯定没100KB,所以不可能把固件放到RAM里统一算CRC,需要分段读取然后做计算,最终得出整个固件的CRC值.

先贴一下我使用的CRC计算的函数.

static const uint32_t crc32_table_0xEDB88320[] = {
0x00000000,0x77073096,0xee0e612c,0x990951ba,0x076dc419,
0x706af48f,0xe963a535,0x9e6495a3,0x0edb8832,0x79dcb8a4,
0xe0d5e91e,0x97d2d988,0x09b64c2b,0x7eb17cbd,0xe7b82d07,
0x90bf1d91,0x1db71064,0x6ab020f2,0xf3b97148,0x84be41de,
0x1adad47d,0x6ddde4eb,0xf4d4b551,0x83d385c7,0x136c9856,
0x646ba8c0,0xfd62f97a,0x8a65c9ec,0x14015c4f,0x63066cd9,
0xfa0f3d63,0x8d080df5,0x3b6e20c8,0x4c69105e,0xd56041e4,
0xa2677172,0x3c03e4d1,0x4b04d447,0xd20d85fd,0xa50ab56b,
0x35b5a8fa,0x42b2986c,0xdbbbc9d6,0xacbcf940,0x32d86ce3,
0x45df5c75,0xdcd60dcf,0xabd13d59,0x26d930ac,0x51de003a,
0xc8d75180,0xbfd06116,0x21b4f4b5,0x56b3c423,0xcfba9599,
0xb8bda50f,0x2802b89e,0x5f058808,0xc60cd9b2,0xb10be924,
0x2f6f7c87,0x58684c11,0xc1611dab,0xb6662d3d,0x76dc4190,
0x01db7106,0x98d220bc,0xefd5102a,0x71b18589,0x06b6b51f,
0x9fbfe4a5,0xe8b8d433,0x7807c9a2,0x0f00f934,0x9609a88e,
0xe10e9818,0x7f6a0dbb,0x086d3d2d,0x91646c97,0xe6635c01,
0x6b6b51f4,0x1c6c6162,0x856530d8,0xf262004e,0x6c0695ed,
0x1b01a57b,0x8208f4c1,0xf50fc457,0x65b0d9c6,0x12b7e950,
0x8bbeb8ea,0xfcb9887c,0x62dd1ddf,0x15da2d49,0x8cd37cf3,
0xfbd44c65,0x4db26158,0x3ab551ce,0xa3bc0074,0xd4bb30e2,
0x4adfa541,0x3dd895d7,0xa4d1c46d,0xd3d6f4fb,0x4369e96a,
0x346ed9fc,0xad678846,0xda60b8d0,0x44042d73,0x33031de5,
0xaa0a4c5f,0xdd0d7cc9,0x5005713c,0x270241aa,0xbe0b1010,
0xc90c2086,0x5768b525,0x206f85b3,0xb966d409,0xce61e49f,
0x5edef90e,0x29d9c998,0xb0d09822,0xc7d7a8b4,0x59b33d17,
0x2eb40d81,0xb7bd5c3b,0xc0ba6cad,0xedb88320,0x9abfb3b6,
0x03b6e20c,0x74b1d29a,0xead54739,0x9dd277af,0x04db2615,
0x73dc1683,0xe3630b12,0x94643b84,0x0d6d6a3e,0x7a6a5aa8,
0xe40ecf0b,0x9309ff9d,0x0a00ae27,0x7d079eb1,0xf00f9344,
0x8708a3d2,0x1e01f268,0x6906c2fe,0xf762575d,0x806567cb,
0x196c3671,0x6e6b06e7,0xfed41b76,0x89d32be0,0x10da7a5a,
0x67dd4acc,0xf9b9df6f,0x8ebeeff9,0x17b7be43,0x60b08ed5,
0xd6d6a3e8,0xa1d1937e,0x38d8c2c4,0x4fdff252,0xd1bb67f1,
0xa6bc5767,0x3fb506dd,0x48b2364b,0xd80d2bda,0xaf0a1b4c,
0x36034af6,0x41047a60,0xdf60efc3,0xa867df55,0x316e8eef,
0x4669be79,0xcb61b38c,0xbc66831a,0x256fd2a0,0x5268e236,
0xcc0c7795,0xbb0b4703,0x220216b9,0x5505262f,0xc5ba3bbe,
0xb2bd0b28,0x2bb45a92,0x5cb36a04,0xc2d7ffa7,0xb5d0cf31,
0x2cd99e8b,0x5bdeae1d,0x9b64c2b0,0xec63f226,0x756aa39c,
0x026d930a,0x9c0906a9,0xeb0e363f,0x72076785,0x05005713,
0x95bf4a82,0xe2b87a14,0x7bb12bae,0x0cb61b38,0x92d28e9b,
0xe5d5be0d,0x7cdcefb7,0x0bdbdf21,0x86d3d2d4,0xf1d4e242,
0x68ddb3f8,0x1fda836e,0x81be16cd,0xf6b9265b,0x6fb077e1,
0x18b74777,0x88085ae6,0xff0f6a70,0x66063bca,0x11010b5c,
0x8f659eff,0xf862ae69,0x616bffd3,0x166ccf45,0xa00ae278,
0xd70dd2ee,0x4e048354,0x3903b3c2,0xa7672661,0xd06016f7,
0x4969474d,0x3e6e77db,0xaed16a4a,0xd9d65adc,0x40df0b66,
0x37d83bf0,0xa9bcae53,0xdebb9ec5,0x47b2cf7f,0x30b5ffe9,
0xbdbdf21c,0xcabac28a,0x53b39330,0x24b4a3a6,0xbad03605,
0xcdd70693,0x54de5729,0x23d967bf,0xb3667a2e,0xc4614ab8,
0x5d681b02,0x2a6f2b94,0xb40bbe37,0xc30c8ea1,0x5a05df1b,
0x2d02ef8d,};

uint32_t soft_crc32(const void *pdata,uint32_t data_size,uint32_t crc)
{
	const uint8_t *data = pdata;
	unsigned int result = crc;
	unsigned char crc_H8;

	while (data_size--) {
		crc_H8 = (unsigned char)(result & 0x000000FF);
		result >>= 8;
		result ^= crc32_table_0xEDB88320[crc_H8 ^ (*data)];
		data++;
	}

	return result;
}

可以看函数中的计算过程,就是一个while循环,按字节去处理.那么要分段就比较容易了.调用函数的时候,给参数"crc"上一次的crc计算结果,然后让函数在这两个初始结果上计算指定字节的数据,这样每次读取完一部分固件数据的时候调一次这个函数,那在最后一次读取固件数据后,最后一次调用这个函数出来的结果就是整个固件的CRC值了.