Piecewise linear interpolation in C++

piecewise_linear_interpolate.cpp

#include <iostream>
#include <map>

using namespace std;

float piecewise_linear_interpolate(map<float, float> value_mappings, float input);

int main() {
    map<float, float> voltage_to_percent_mapping {
        { 09.5, 0.0 },
        { 10.8, 1.00 },
        { 12.8, 10.00 },
        { 12.9, 20.00 },
        { 13.0, 30.00 },
        { 13.1, 40.00 },
        { 13.2, 70.00 },
        { 13.3, 90.00 },
        { 13.4, 99.00 },
        { 13.5, 100.00 }
    };

    cout << piecewise_linear_interpolate(voltage_to_percent_mapping, 12.56) << endl;

    return 0;
}

float piecewise_linear_interpolate(map<float, float> m, float input) {
    // Out of bounds (too low)
    if (input < m.begin()->first) {
        return m.begin()->second;
    }

    // Out of bounds (too high)
    if (input > m.rbegin()->first) {
        return m.rbegin()->second;
    }

    // Find the two nearest values and interpolate between them
    for (auto it = m.begin(); it != m.end(); ++it) {
        if (input > it->first && input < next(it)->first) {
            float x1 = it->first;
            float y1 = it->second;
            float x2 = next(it)->first;
            float y2 = next(it)->second;
            float slope = (y2 - y1) / (x2 - x1);
            float y_intercept = y1 - (slope * x1);
            return (slope * input) + y_intercept;
        }
    }

    // Fallback (should never happen)
    return 0.0;
}