87 lines
2.7 KiB
C++
87 lines
2.7 KiB
C++
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#include <map>
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#include "vtr_assert.h"
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#include "vtr_error.h"
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#include "vtr_math.h"
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namespace vtr {
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int ipow(int base, int exp) {
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int result = 1;
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VTR_ASSERT(exp >= 0);
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while (exp) {
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if (exp & 1)
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result *= base;
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exp >>= 1;
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base *= base;
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}
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return result;
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}
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/* Performs linear interpolation or extrapolation on the set of (x,y) values specified by the xy_map.
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A requested x value is passed in, and we return the interpolated/extrapolated y value at this requested value of x.
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Meant for maps where both key and element are numbers.
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This is specifically enforced by the explicit instantiations below this function. i.e. only templates
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using those types listed in the explicit instantiations below are allowed */
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template<typename X, typename Y> Y linear_interpolate_or_extrapolate(const std::map<X,Y> *xy_map, X requested_x){
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Y result;
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/* the intention of this function is to interpolate/extrapolate. we can't do so with less than 2 values in the xy_map */
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if (xy_map->size() < 2){
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throw VtrError("linear_interpolate_or_extrapolate: cannot interpolate/extrapolate based on less than 2 (x,y) pairs", __FILE__, __LINE__);
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}
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auto itr = xy_map->find(requested_x);
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if (itr != xy_map->end()){
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/* requested x already exists in the x,y map */
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result = itr->second;
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} else {
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/* requested x does not exist in the x,y map. need to interpolate/extrapolate */
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typename std::map<X,Y>::const_iterator it;
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double x_low, x_high, y_low, y_high;
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double slope, reference_y, delta_x;
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/* get first x greater than the one requested */
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it = xy_map->upper_bound(requested_x);
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if(it == xy_map->end()){
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/* need to extrapolate to higher x. based on the y values at the two largest x values */
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it--;
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x_high = (double)it->first;
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y_high = (double)it->second;
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it--;
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x_low = (double)it->first;
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y_low = (double)it->second;
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} else if (it == xy_map->begin()){
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/* need to extrapolate to lower x. based on the y values at the two smallest x */
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x_low = (double)it->first;
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y_low = (double)it->second;
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it++;
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x_high = (double)it->first;
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y_high = (double)it->second;
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} else {
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/* need to interpolate. based on y values at x just above/below
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the one we want */
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x_high = (double)it->first;
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y_high = (double)it->second;
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it--;
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x_low = (double)it->first;
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y_low = (double)it->second;
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}
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slope = (y_high - y_low) / (x_high - x_low);
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reference_y = y_low;
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delta_x = (double)requested_x - x_low;
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result = (Y)(reference_y + (slope * delta_x));
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}
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return result;
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}
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template double linear_interpolate_or_extrapolate(const std::map<int,double> *xy_map, int requested_x); /* (int,double) */
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template double linear_interpolate_or_extrapolate(const std::map<double,double> *xy_map, double requested_x); /* (double,double) */
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}
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