/**
 * \file
 *
 * \brief Hamming ECC software implementation.
 *
 * This file contains a software Hamming ECC implementation.
 *
 * Copyright (c) 2012-2015 Atmel Corporation. All rights reserved.
 *
 * \asf_license_start
 *
 * \page License
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * 3. The name of Atmel may not be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * 4. This software may only be redistributed and used in connection with an
 *    Atmel microcontroller product.
 *
 * THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
 * EXPRESSLY AND SPECIFICALLY DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * \asf_license_stop
 *
 */
/*
 * Support and FAQ: visit <a href="http://www.atmel.com/design-support/">Atmel Support</a>
 */

#include "ecc-sw.h"

/**
 *  Count and return the number of bits set to '1' in the given byte.
 *
 *  \param byte  Byte to count.
 */
static uint32_t count_bits_in_byte(uint8_t byte)
{
	uint32_t count = 0;

	while (byte > 0) {
		if (byte & 1) {
			count++;
		}
		byte >>= 1;
	}

	return count;
}

/**
 *  Count and return the number of bits set to '1' in the given hamming code.
 *
 *  \param code  Hamming code.
 */
static uint32_t count_bits_in_code256(uint8_t *code)
{
	return count_bits_in_byte(code[0]) + count_bits_in_byte(code[1]) +
			count_bits_in_byte(code[2]);
}

/**
 *  Calculates the 22-bit hamming code for a 256-bytes block of data.
 *
 *  \param data  Data buffer to calculate code for.
 *  \param code  Pointer to a buffer where the code should be stored.
 */
static void compute256(const uint8_t *data, uint8_t *code)
{
	uint32_t i;
	uint8_t column_sum = 0;
	uint8_t even_line_code = 0;
	uint8_t odd_line_code = 0;
	uint8_t even_column_code = 0;
	uint8_t odd_column_code = 0;

	/* 
	 * Xor all bytes together to get the column sum.
	 * At the same time, calculate the even and odd line codes.
	 */
	for (i = 0; i < 256; i++) {
		column_sum ^= data[i];

		/* 
		 * If the xor sum of the byte is 0, then this byte has no incidence on
		 * the computed code. So check if the sum is 1.
		 */
		if ((count_bits_in_byte(data[i]) & 1) == 1) {
			/*
			 * Parity groups are formed by forcing a particular index bit to 0
			 * (even) or 1 (odd).
			 * Example on one byte:
			 *
			 * bits (dec)  7   6   5   4   3   2   1   0
			 *      (bin) 111 110 101 100 011 010 001 000
			 *                            '---'---'---'----------.
			 *                                                   |
			 * groups P4' ooooooooooooooo eeeeeeeeeeeeeee P4     |
			 *        P2' ooooooo eeeeeee ooooooo eeeeeee P2     |
			 *        P1' ooo eee ooo eee ooo eee ooo eee P1     |
			 *                                                   |
			 * We can see that:                                  |
			 *  - P4  -> bit 2 of index is 0 --------------------'
			 *  - P4' -> bit 2 of index is 1.
			 *  - P2  -> bit 1 of index if 0.
			 *  - etc...
			 * We deduce that a bit position has an impact on all even Px if
			 * the log2(x)nth bit of its index is 0
			 *     ex: log2(4) = 2, bit2 of the index must be 0 (-> 0 1 2 3)
			 * and on all odd Px' if the log2(x)nth bit of its index is 1
			 *     ex: log2(2) = 1, bit1 of the index must be 1 (-> 0 1 4 5)
			 *
			 * As such, we calculate all the possible Px and Px' values at the
			 * same time in two variables, even_line_code and odd_line_code, such as
			 *     even_line_code bits: P128  P64  P32  P16  P8  P4  P2  P1
			 *     odd_line_code  bits: P128' P64' P32' P16' P8' P4' P2' P1'
			 */
			even_line_code ^= (255 - i);
			odd_line_code ^= i;
		}
	}

	/*
	 * At this point, we have the line parities, and the column sum. First, We
	 * must calculate the parity group values on the column sum.
	 */
	for (i = 0; i < 8; i++) {
		if (column_sum & 1) {
			even_column_code ^= (7 - i);
			odd_column_code ^= i;
		}
		column_sum >>= 1;
	}

	/*
	 * Now, we must interleave the parity values, to obtain the following layout:
	 * Code[0] = Line1
	 * Code[1] = Line2
	 * Code[2] = Column
	 * Line = Px' Px P(x-1)- P(x-1) ...
	 * Column = P4' P4 P2' P2 P1' P1 PadBit PadBit
	 */
	code[0] = 0;
	code[1] = 0;
	code[2] = 0;

	for (i = 0; i < 4; i++) {
		code[0] <<= 2;
		code[1] <<= 2;
		code[2] <<= 2;

		/* Line 1 */
		if ((odd_line_code & 0x80) != 0) {
			code[0] |= 2;
		}

		if ((even_line_code & 0x80) != 0) {
			code[0] |= 1;
		}
		/* Line 2 */
		if ((odd_line_code & 0x08) != 0) {
			code[1] |= 2;
		}

		if ((even_line_code & 0x08) != 0) {
			code[1] |= 1;
		}
		/* Column */
		if ((odd_column_code & 0x04) != 0) {
			code[2] |= 2;
		}

		if ((even_column_code & 0x04) != 0) {
			code[2] |= 1;
		}

		odd_line_code <<= 1;
		even_line_code <<= 1;
		odd_column_code <<= 1;
		even_column_code <<= 1;
	}

	/* Invert codes (linux compatibility) */
	code[0] = (~(uint32_t) code[0]);
	code[1] = (~(uint32_t) code[1]);
	code[2] = (~(uint32_t) code[2]);

}

/**
 *  Verifies and corrects a 256-bytes block of data using the given 22-bits
 *  hamming code.
 *
 *  \param puc_data  Pointer to data buffer to check.
 *  \param puc_original_code  Pointer to hamming code to use for verifying the data.
 *
 *  \return 0 if there is no error, otherwise returns a HAMMING_ERROR code.
 */
static uint32_t verify256(uint8_t *puc_data, const uint8_t *puc_original_code)
{
	/* Calculate new code */
	uint8_t computed_code[3];
	uint8_t correction_code[3];

	compute256(puc_data, computed_code);

	/* Xor both codes together */
	correction_code[0] = computed_code[0] ^ puc_original_code[0];
	correction_code[1] = computed_code[1] ^ puc_original_code[1];
	correction_code[2] = computed_code[2] ^ puc_original_code[2];


	/* If all bytes are 0, there is no error */
	if ((correction_code[0] == 0) && (correction_code[1] == 0)
			&& (correction_code[2] == 0)) {
		return 0;
	}

	/* If there is a single bit error, there are 11 bits set to 1 */
	if (count_bits_in_code256(correction_code) == 11) {
		/* Get byte and bit indexes */
		uint8_t byte;
		uint8_t bit;

		byte = correction_code[0] & 0x80;
		byte |= ((correction_code[0] << 1) & 0x40);
		byte |= ((correction_code[0] << 2) & 0x20);
		byte |= ((correction_code[0] << 3) & 0x10);

		byte |= ((correction_code[1] >> 4) & 0x08);
		byte |= ((correction_code[1] >> 3) & 0x04);
		byte |= ((correction_code[1] >> 2) & 0x02);
		byte |= ((correction_code[1] >> 1) & 0x01);

		bit = (correction_code[2] >> 5) & 0x04;
		bit |= ((correction_code[2] >> 4) & 0x02);
		bit |= ((correction_code[2] >> 3) & 0x01);

		/* Correct bit */
		puc_data[byte] ^= (1 << bit);

		return HAMMING_ERROR_SINGLE_BIT;
	}

	/* Check if ECC has been corrupted */
	if (count_bits_in_code256(correction_code) == 1) {
		return HAMMING_ERROR_ECC;
	}
	/* Otherwise, this is a multi-bit error */
	else {
		return HAMMING_ERROR_MULTIPLE_BITS;
	}
}

/**
 *  Computes 3-bytes hamming codes for a data block whose size is multiple of
 *  256 bytes. Each 256 bytes block gets its own code.
 *
 *  \param puc_data Pointer to data to compute code for.
 *  \param dw_size  Data size in bytes.
 *  \param puc_code Pointer to codes buffer.
 */
void hamming_compute_256x(const uint8_t *puc_data, uint32_t dw_size,
		uint8_t *puc_code)
{
	while (dw_size > 0) {
		compute256(puc_data, puc_code);

		puc_data += 256;
		puc_code += 3;
		dw_size -= 256;
	}
}

/**
 *  Verify 3-bytes hamming codes for a data block whose size is multiple of
 *  256 bytes. Each 256-bytes block is verified with its own code.
 *
 *  \param puc_data Pointer to data buffer to verify.
 *  \param dw_size  Size of the data in bytes.
 *  \param puc_code Pointer to original codes.
 *
 *  \return 0 if the data is correct, HAMMING_ERROR_SINGLE_BIT if one or more
 *  block(s) have had a single bit corrected, or either HAMMING_ERROR_ECC
 *  or HAMMING_ERROR_MULTIPLE_BITS.
 */
uint32_t hamming_verify_256x(uint8_t *puc_data, uint32_t dw_size,
		const uint8_t *puc_code)
{
	uint32_t error;
	uint32_t result = 0;

	while (dw_size > 0) {
		error = verify256(puc_data, puc_code);

		if (error == HAMMING_ERROR_SINGLE_BIT) {
			result = HAMMING_ERROR_SINGLE_BIT;
		} else {
			if (error) {
				return error;
			}
		}

		puc_data += 256;
		puc_code += 3;
		dw_size -= 256;
	}

	return result;
}