#include "crc16_dnp.h"

/**
 * Static table used for the table_driven implementation.
 */
static const crc16_t crc16_dnp_table[256] = {
	0x0000,  0x365e,  0x6cbc,  0x5ae2,  0xd978,  0xef26,  0xb5c4,  0x839a,
	0xff89,  0xc9d7,  0x9335,  0xa56b,  0x26f1,  0x10af,  0x4a4d,  0x7c13,
	0xb26b,  0x8435,  0xded7,  0xe889,  0x6b13,  0x5d4d,  0x07af,  0x31f1,
	0x4de2,  0x7bbc,  0x215e,  0x1700,  0x949a,  0xa2c4,  0xf826,  0xce78,
	0x29af,  0x1ff1,  0x4513,  0x734d,  0xf0d7,  0xc689,  0x9c6b,  0xaa35,
	0xd626,  0xe078,  0xba9a,  0x8cc4,  0x0f5e,  0x3900,  0x63e2,  0x55bc,
	0x9bc4,  0xad9a,  0xf778,  0xc126,  0x42bc,  0x74e2,  0x2e00,  0x185e,
	0x644d,  0x5213,  0x08f1,  0x3eaf,  0xbd35,  0x8b6b,  0xd189,  0xe7d7,
	0x535e,  0x6500,  0x3fe2,  0x09bc,  0x8a26,  0xbc78,  0xe69a,  0xd0c4,
	0xacd7,  0x9a89,  0xc06b,  0xf635,  0x75af,  0x43f1,  0x1913,  0x2f4d,
	0xe135,  0xd76b,  0x8d89,  0xbbd7,  0x384d,  0x0e13,  0x54f1,  0x62af,
	0x1ebc,  0x28e2,  0x7200,  0x445e,  0xc7c4,  0xf19a,  0xab78,  0x9d26,
	0x7af1,  0x4caf,  0x164d,  0x2013,  0xa389,  0x95d7,  0xcf35,  0xf96b,
	0x8578,  0xb326,  0xe9c4,  0xdf9a,  0x5c00,  0x6a5e,  0x30bc,  0x06e2,
	0xc89a,  0xfec4,  0xa426,  0x9278,  0x11e2,  0x27bc,  0x7d5e,  0x4b00,
	0x3713,  0x014d,  0x5baf,  0x6df1,  0xee6b,  0xd835,  0x82d7,  0xb489,
	0xa6bc,  0x90e2,  0xca00,  0xfc5e,  0x7fc4,  0x499a,  0x1378,  0x2526,
	0x5935,  0x6f6b,  0x3589,  0x03d7,  0x804d,  0xb613,  0xecf1,  0xdaaf,
	0x14d7,  0x2289,  0x786b,  0x4e35,  0xcdaf,  0xfbf1,  0xa113,  0x974d,
	0xeb5e,  0xdd00,  0x87e2,  0xb1bc,  0x3226,  0x0478,  0x5e9a,  0x68c4,
	0x8f13,  0xb94d,  0xe3af,  0xd5f1,  0x566b,  0x6035,  0x3ad7,  0x0c89,
	0x709a,  0x46c4,  0x1c26,  0x2a78,  0xa9e2,  0x9fbc,  0xc55e,  0xf300,
	0x3d78,  0x0b26,  0x51c4,  0x679a,  0xe400,  0xd25e,  0x88bc,  0xbee2,
	0xc2f1,  0xf4af,  0xae4d,  0x9813,  0x1b89,  0x2dd7,  0x7735,  0x416b,
	0xf5e2,  0xc3bc,  0x995e,  0xaf00,  0x2c9a,  0x1ac4,  0x4026,  0x7678,
	0x0a6b,  0x3c35,  0x66d7,  0x5089,  0xd313,  0xe54d,  0xbfaf,  0x89f1,
	0x4789,  0x71d7,  0x2b35,  0x1d6b,  0x9ef1,  0xa8af,  0xf24d,  0xc413,
	0xb800,  0x8e5e,  0xd4bc,  0xe2e2,  0x6178,  0x5726,  0x0dc4,  0x3b9a,
	0xdc4d,  0xea13,  0xb0f1,  0x86af,  0x0535,  0x336b,  0x6989,  0x5fd7,
	0x23c4,  0x159a,  0x4f78,  0x7926,  0xfabc,  0xcce2,  0x9600,  0xa05e,
	0x6e26,  0x5878,  0x029a,  0x34c4,  0xb75e,  0x8100,  0xdbe2,  0xedbc,
	0x91af,  0xa7f1,  0xfd13,  0xcb4d,  0x48d7,  0x7e89,  0x246b,  0x1235
};

crc16_t crc16_dnp_update(crc16_t crc, const void *data, size_t data_len)
{
	const unsigned char *d = (const unsigned char *)data;
	unsigned int tbl_idx;

	while (data_len--)
	{
		tbl_idx = (crc ^ *d) & 0xff;
		crc = (crc << 8) ^ crc16_dnp_table[tbl_idx];
		d++;
	}

	return crc & 0xffff;
}