[avr-gcc-list] Help with flash lookup table

[Micah Carrick]

I'm a bit new to this.  I'm trying to use a lookup table in flash memory 
to determine the distance from the ADC from a GP2D120 distance sensor.  
I basically have this:

static uint8_t gp2d120_data[] PROGMEM = {
       
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,30,30,29,28,
       
27,26,25,25,24,24,24,23,23,23,22,22,21,20,20,19,19,19,19,18,18,18,17,17,
       
17,16,16,16,15,15,15,15,15,14,14,14,13,13,13,13,13,13,12,12,12,12,12,12,
       
11,11,11,11,11,11,10,10,10,10,10,10,10,9,9,9,9,9,9,9,9,9,8,8,8,8,8,8,8,
       
8,8,8,8,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
       
6,6,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
       
4,4,4,4,4,4,4,4,4,4,4,4,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,2,2,2,
       
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2
};

uint8_t gp2d120_adc8_to_cm (uint8_t adc_value)
{
       uint8_t *ptr = gp2d120_data;
       *ptr += adc_value;
      
       return pgm_read_byte(ptr);
}

I believe my function there isn't quite right.  Can someone point me in 
the right direction?