#include <stdio.h>
#include <stdint.h>

typedef struct
{
    void* userData;
    float (*value)(void*, int);
} IA;

float get_float_from_uint16(void* userData, int index)
{
    return ((uint16_t*) userData)[index];
}

int main()
{
    uint16_t bytes[] = {1, 2, 3, 4, 5 }; 
    IA a = {bytes, &get_float_from_uint16};

    int index = 0;
    float f = a.value(a.userData, index);
    printf("%f\n", f);
}