fast_math.c

#include <math.h>
#include "fast_math.h"
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

float x_to_index(float x, fast_math_function_t* fast_math_struct) {
    return fast_math_struct->x2id_coef * (x - fast_math_struct->start_value);
}

float index_to_x(uint16_t index, fast_math_function_t* fast_math_struct) {
    return ((float)index) * fast_math_struct->id2x_coef + fast_math_struct->start_value;
}

fast_math_function_t fast_math_init(float (*target_function)(float), float start_value, float end_value, int32_t samples_n) {
    float x2id_coef = (samples_n - 1) / (end_value - start_value);
    float id2x_coef = (end_value - start_value) / (samples_n - 1);
    float* function_values = (float*)malloc(samples_n * sizeof(float));

    fast_math_function_t fast_math_struct = {
        .start_value = start_value,
        .end_value = end_value,
        .id2x_coef = id2x_coef,
        .x2id_coef = x2id_coef,
        .function_values = function_values
    };

    for (uint16_t index = 0; index < samples_n; index++) {
        float x = index_to_x(index, &fast_math_struct);
        float value = target_function(x);
        function_values[index] = value;
    }

    return fast_math_struct;
}

float fast_math_get(float x, fast_math_function_t* fast_math_struct) {
    if (x >= fast_math_struct->end_value) {
        int32_t end_index = x_to_index(fast_math_struct->end_value, fast_math_struct);
        return fast_math_struct->function_values[end_index];
    }
    else if (x <= fast_math_struct->start_value) {
        int32_t start_index = x_to_index(fast_math_struct->start_value, fast_math_struct);
        return fast_math_struct->function_values[start_index];
    }

    float index = x_to_index(x, fast_math_struct);
    uint16_t index1 = (uint16_t)index;
    uint16_t index2 = (uint16_t)index1 + 1;
    float w = index - (float)index1;

    return fast_math_struct->function_values[index1] + w * (fast_math_struct->function_values[index2] - fast_math_struct->function_values[index1]);
}