Programming Specification

int return_code = 0;

exit_flag:
	if(m_a)
		free(m_a);
	if(m_b)
		free(m_b);
	if(m_c)
		free(m_c);
	if(m_d)
		free(m_d);

	return return_code;

//check
if (NULL == a) {
	return_code = -1;
	goto exit_flag;
}
if (NULL == b) {
	return_code = -1;
	goto exit_flag;
}

// allocate memory
m_a = (float *) malloc(n * sizeof(float));
if(!m_a){
	printf("Failed to allocate memory! \n");
	return_code = -1;
	goto exit_flag;
}

#define IN
#define OUT

int solve_tridiagonal_equation_thomas(
	IN int n,
	IN float a[], IN float b[], IN float c[],
	IN float d[],
	OUT float x[]
)
{
	int return_code = 0;

	//check
	if (NULL == a) {
		return_code = -1;
		goto exit_flag;
	}
	if (NULL == b) {
		return_code = -1;
		goto exit_flag;
	}
	if (NULL == c) {
		return_code = -1;
		goto exit_flag;
	}
	if (NULL == d) {
		return_code = -1;
		goto exit_flag;
	}
	if (NULL == x) {
		return_code = -1;
		goto exit_flag;
	}


	int i = 0;
	float tmp = 0;
	float *m_a, *m_b, *m_c, *m_d;

	// allocate memory
	m_a = (float *) malloc(n * sizeof(float));
	if(!m_a){
		printf("Failed to allocate memory! \n");
		return_code = -1;
		goto exit_flag;
	}
	m_b = (float *) malloc(n * sizeof(float));
	if(!m_b){
		printf("Failed to allocate memory! \n");
		return_code = -1;
		goto exit_flag;
	}
	m_c = (float *) malloc(n * sizeof(float));
	if(!m_c){
		printf("Failed to allocate memory! \n");
		return_code = -1;
		goto exit_flag;
	}
	m_d = (float *) malloc(n * sizeof(float));
	if(!m_d){
		printf("Failed to allocate memory! \n");
		return_code = -1;
		goto exit_flag;
	}


	// diagonal dominant validation and copy data
	bool cond1 = (abs(b[0]) > abs(c[0])) && (abs(c[0]) > 0);
	bool cond2 = (abs(b[n-1]) > abs(a[n-1])) && (abs(a[n-1]) > 0);
	
	if(!(cond1 && cond2))
	{
		printf("Matrix is Invalid! \n");
		return_code = -2;
		goto exit_flag;
	}

	for(i = 1; i < n-1; ++i)
	{
		if(abs(b[i]) < abs(c[i]) + abs(c[i]))
		{
			printf("Matrix is NOT diagonal dominant! \n");
			return_code = -2;
			goto exit_flag;
		}
		else{
			m_a[i] = a[i];
			m_b[i] = b[i];
			m_c[i] = c[i];
			m_d[i] = d[i];
		}
	}
	memcpy(m_a, a, n * sizeof(float));


	// forward elimination
	for(i = 1; i < n; ++i)
	{
		tmp = m_a[i] / m_b[i-1];
		m_b[i] = m_b[i] - tmp * m_c[i-1];
		m_d[i] = m_d[i] - tmp * m_d[i-1];
	}

	// backward substitution
	x[n-1] = m_d[n-1] / m_b[n-1];
	for(i = n-2; i >= 0; --i)
	{
		x[i] = (m_d[i] - m_c[i] * x[i+1]) / m_b[i];
	}

	// free memory and exit
exit_flag:
	if(m_a)
		free(m_a);
	if(m_b)
		free(m_b);
	if(m_c)
		free(m_c);
	if(m_d)
		free(m_d);

	return return_code;
}