Simple compression Algorithm in C is not working..any suggestions?

Question

I am creating a project in nordic Micro that reads a value from an Analog input termninal an output it into UART. I am now trying to compress the data using GE Proficy Historian Compression so that only changed data are outputted in the UART. But my code is not working. Outputted data are sometime still redundant. The idea of the program is to generate an interrupt every certain amout of time, read the adc value and if its different than previous value, output it to the UART port. the algorithm is explained here http://www.evsystems.net/files/GE_Historian_Compression_Overview.ppt The main portion of the code that handles the interrupt is as shown below

void ADC_IRQHandler(void)
{
    /* Clear dataready event */
  NRF_ADC->EVENTS_END = 0;   
    // write ADC value to UART port 

    // Compression Algorithm should occur here
    uint8_t current_Val= NRF_ADC->RESULT;
    //simple_uart_put(current_evaluation);


    // Construct error bands around the held point

    float U_tolerance = current_Val  + error_tolerance;
    float L_tolerance = current_Val - error_tolerance; // integer type is selected since lower tolerance could be negative

    if( first_Run == false)
    {
        float slope = ((current_Val - Archived_Val) / (held_Time - Archived_Time)) ;
        if (slope > U_Slope || slope > L_Slope)
        {
            Archived_Val = current_Val; // update the archived value
            held_Time = 1; // reset held time
            simple_uart_put(current_Val);
            first_Run = true;
            Archived_Val = current_Val;
        }
        else
        {
            float Upper_Slope = (U_tolerance - Archived_Val) /( held_Time - Archived_Time);
            float Lower_Slope  = (L_tolerance - Archived_Val)/(held_Time- Archived_Time);

            if(Upper_Slope < U_Slope) // lowest upper slope is always taken as a blanket boundry
            {
                U_Slope = Upper_Slope;
            }
            if(Lower_Slope < L_Slope)
            {
                L_Slope = Lower_Slope;
            }
            held_Time += time_increment;
        }
    }

    if (first_Run == true) // first held point always outputted
    {
            // calculate the slopes of the two lines 
    float Upper_Slope = (U_tolerance - Start_Up_Val) /( held_Time - Archived_Time);
    float Lower_Slope  = (L_tolerance - Start_Up_Val)/(held_Time- Archived_Time);

        // Update Max and Min slopes

    if(Upper_Slope < U_Slope) // lowest upper slope is always taken as a blanket boundry
    {
            U_Slope = Upper_Slope;
    }
    if(Lower_Slope < L_Slope)
    {
        L_Slope = Lower_Slope;
    }


    held_Time += time_increment;
    first_Run = false;
    Archived_Val = current_Val;
    }

}

The veriables are defined as follow

> uint32_t error_tolerance = 50; // error tolerance value for swining door algorithm
uint8_t Start_Up_Val = 100;
float held_Time = 1;
int Archived_Time = 0;
float U_Slope = 2500;
float L_Slope = 0;
//float slope;
uint8_t Archived_Val;
bool GE_Comp(uint8_t, uint8_t, uint8_t, int);
bool first_Run = true;
float time_increment = 0.1;

Answer 1

Thank you all for your contribution and mostly to @Weather Vane . It was exactly as you and others suggested, the interrupt handler was executing too much coding which prohibited it from proper functionality. I now fixed the problem by diverging the parts of the code to the main function as suggested. Regareds