crc7.c

static u8 crc7(const u8 *data, u32 len)
{
	u32 crc = 0; // u32 to avoid "and rX, rX, #0xFF" in the bit loop.
	while(len--)
	{
		crc ^= *data++;
		for(u32 i = 0; i < 8; i++)
		{
			if(crc & 0x80u) crc ^= 0x89u;
			crc <<= 1;
		}
	}

	return crc | 1u;
}

void calcCrc7Table(void)
{
	for(u32 i = 0; i < 256; i++)
	{
		u32 crc = i; // u32 to avoid "and rX, rX, #0xFF" in the bit loop.
		for(u32 i = 0; i < 8; i++)
		{
			if(crc & 0x80u) crc ^= 0x89u;
			crc <<= 1;
		}
		g_crc7ByteTable[i] = crc;
	}
}

u8 byte_crc7(const void *data, u32 len)
{
	const u8 *ptr8 = (const u8*)data;

	static constexpr u8 crc7Table[256] =
	{
		0x00, 0x12, 0x24, 0x36, 0x48, 0x5A, 0x6C, 0x7E, 0x90, 0x82, 0xB4, 0xA6, 0xD8, 0xCA, 0xFC, 0xEE,
		0x32, 0x20, 0x16, 0x04, 0x7A, 0x68, 0x5E, 0x4C, 0xA2, 0xB0, 0x86, 0x94, 0xEA, 0xF8, 0xCE, 0xDC,
		0x64, 0x76, 0x40, 0x52, 0x2C, 0x3E, 0x08, 0x1A, 0xF4, 0xE6, 0xD0, 0xC2, 0xBC, 0xAE, 0x98, 0x8A,
		0x56, 0x44, 0x72, 0x60, 0x1E, 0x0C, 0x3A, 0x28, 0xC6, 0xD4, 0xE2, 0xF0, 0x8E, 0x9C, 0xAA, 0xB8,
		0xC8, 0xDA, 0xEC, 0xFE, 0x80, 0x92, 0xA4, 0xB6, 0x58, 0x4A, 0x7C, 0x6E, 0x10, 0x02, 0x34, 0x26,
		0xFA, 0xE8, 0xDE, 0xCC, 0xB2, 0xA0, 0x96, 0x84, 0x6A, 0x78, 0x4E, 0x5C, 0x22, 0x30, 0x06, 0x14,
		0xAC, 0xBE, 0x88, 0x9A, 0xE4, 0xF6, 0xC0, 0xD2, 0x3C, 0x2E, 0x18, 0x0A, 0x74, 0x66, 0x50, 0x42,
		0x9E, 0x8C, 0xBA, 0xA8, 0xD6, 0xC4, 0xF2, 0xE0, 0x0E, 0x1C, 0x2A, 0x38, 0x46, 0x54, 0x62, 0x70,
		0x82, 0x90, 0xA6, 0xB4, 0xCA, 0xD8, 0xEE, 0xFC, 0x12, 0x00, 0x36, 0x24, 0x5A, 0x48, 0x7E, 0x6C,
		0xB0, 0xA2, 0x94, 0x86, 0xF8, 0xEA, 0xDC, 0xCE, 0x20, 0x32, 0x04, 0x16, 0x68, 0x7A, 0x4C, 0x5E,
		0xE6, 0xF4, 0xC2, 0xD0, 0xAE, 0xBC, 0x8A, 0x98, 0x76, 0x64, 0x52, 0x40, 0x3E, 0x2C, 0x1A, 0x08,
		0xD4, 0xC6, 0xF0, 0xE2, 0x9C, 0x8E, 0xB8, 0xAA, 0x44, 0x56, 0x60, 0x72, 0x0C, 0x1E, 0x28, 0x3A,
		0x4A, 0x58, 0x6E, 0x7C, 0x02, 0x10, 0x26, 0x34, 0xDA, 0xC8, 0xFE, 0xEC, 0x92, 0x80, 0xB6, 0xA4,
		0x78, 0x6A, 0x5C, 0x4E, 0x30, 0x22, 0x14, 0x06, 0xE8, 0xFA, 0xCC, 0xDE, 0xA0, 0xB2, 0x84, 0x96,
		0x2E, 0x3C, 0x0A, 0x18, 0x66, 0x74, 0x42, 0x50, 0xBE, 0xAC, 0x9A, 0x88, 0xF6, 0xE4, 0xD2, 0xC0,
		0x1C, 0x0E, 0x38, 0x2A, 0x54, 0x46, 0x70, 0x62, 0x8C, 0x9E, 0xA8, 0xBA, 0xC4, 0xD6, 0xE0, 0xF2
	};

	u8 crc = 0;
	do
	{
		crc = crc7Table[crc ^ *ptr8++];
	} while(--len);

	return crc | 1u;
}