Programming Specification

1. Define variable return_code to record the function's status.

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int return_code = 0;

 

2. Define the exit flag: exit_flag, which is used by goto. This flag is defined at the end of function body. The content of exit_flag includes free memory and return the status of function.

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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;

 

3. Check the array formal parameters of function.

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

 

4. Allocate memory

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

 

Example:

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#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;
}

 

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