code for implementing trigonometric calculation

What "help", exactly, do you need?

Can you just use the standard library functions?
If you can't, you need to explain why - otherwise it's impossible to know which alternatives may be appropriate.

Is this for your accelerometer: http://www.keil.com/forum/21787 ?

from the link, do you mean arctan, then

//*****************************************************/
// Fast arctan2
//*****************************************************/
float CHC_atan(float q, float i)
{
    float angle, abs_q, r, extra;

    abs_q = fabs(q);
    if (i >= 0)
    {
        r = CHC_iMoreThan(abs_q, i);
        extra = 0.7853982f;
    }
    else
    {
        r = CHC_iLessThan(abs_q, i);
        extra = 2.3561945f;
    }
    angle = CHC_fast_atan_calc(r) + extra;
    if (q < 0) angle *= -1;

    return angle;
}
//-----------------------------------------------------

//-----------------------------------------------------
// allocated in hardware
static inline float CHC_iMoreThan(float abs_q, float i)
{
        return ((i - abs_q) / (i + abs_q));
}
//-----------------------------------------------------

//-----------------------------------------------------
// allocated in hardware
static inline float CHC_iLessThan(float abs_q, float i)
{
        return ((i + abs_q) / (abs_q - i));
}
//-----------------------------------------------------

//-----------------------------------------------------
// allocated in hardware
static inline float CHC_fast_atan_calc(float r)
{
        return (0.1963f * r * r * r - 0.9817f * r);
}
//*****************************************************/

actually

//*****************************************************/
// Fast arctan2 software implementation
//*****************************************************/
//float SW_atan(float q, float i)
//{
//    float angle, abs_q, r;
//
//    abs_q = fabs(q) + 1e-10;      // kludge to prevent 0/0 condition
//    if (i >= 0)
//    {
//        r = (i - abs_q) / (i + abs_q);
//        angle = 0.1963f * r * r * r - 0.9817f * r + 0.7853982f;
//    }
//    else
//    {
//        r = (i + abs_q) / (abs_q - i);
//        angle = 0.1963f * r * r * r - 0.9817f * r + 2.3561945f;
//    }
//    if (q < 0) angle *= -1;
//
//    return angle;
//}
//*****************************************************/