/*  Simple ECC verification code, originally by Segher */

#include <stdio.h>
#include <string.h>
#include "amoxiflash.h"

static u8 parity(u8 x)
{
	u8 y = 0;

	while (x) {
		y ^= (x & 1);
		x >>= 1;
	}

	return y;
}

static void calc_ecc(u8 *data, u8 *ecc)
{
	u8 a[12][2];
	int i, j;
	u32 a0, a1;
	u8 x;

	memset(a, 0, sizeof a);
	for (i = 0; i < 512; i++) {
		x = data[i];
		for (j = 0; j < 9; j++)
			a[3+j][(i >> j) & 1] ^= x;
	}

	x = a[3][0] ^ a[3][1];
	a[0][0] = x & 0x55;
	a[0][1] = x & 0xaa;
	a[1][0] = x & 0x33;
	a[1][1] = x & 0xcc;
	a[2][0] = x & 0x0f;
	a[2][1] = x & 0xf0;

	for (j = 0; j < 12; j++) {
		a[j][0] = parity(a[j][0]);
		a[j][1] = parity(a[j][1]);
	}

	a0 = a1 = 0;
	for (j = 0; j < 12; j++) {
		a0 |= a[j][0] << j;
		a1 |= a[j][1] << j;
	}

	ecc[0] = a0;
	ecc[1] = a0 >> 8;
	ecc[2] = a1;
	ecc[3] = a1 >> 8;
}

u8 * calc_page_ecc(u8 *data)
{
	static u8 ecc[16];

	calc_ecc(data, ecc);
	calc_ecc(data + 512, ecc + 4);
	calc_ecc(data + 1024, ecc + 8);
	calc_ecc(data + 1536, ecc + 12);
	return ecc;
}


int check_ecc(u8 *page) {
	u8 *stored_ecc = page + 2048 + 48;
	if (page[2048]!=0xFF) return ECC_INVALID;
	if (stored_ecc[0] == 0xFF && stored_ecc[1] == 0xFF) return ECC_BLANK;
	
	if (memcmp(stored_ecc, calc_page_ecc(page), 16)) return ECC_WRONG;
	return ECC_OK;
}