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/*
* Copyright 2011-2015 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "util_math_cdf.h"
#include "util_algorithm.h"
#include "util_math.h"
CCL_NAMESPACE_BEGIN
/* Invert pre-calculated CDF function. */
void util_cdf_invert(const int resolution,
const float from,
const float to,
const vector<float> &cdf,
const bool make_symmetric,
vector<float> &inv_cdf) {
const float inv_resolution = 1.0f / (float)resolution;
const float range = to - from;
inv_cdf.resize(resolution);
if(make_symmetric) {
const int half_size = (resolution - 1) / 2;
for(int i = 0; i <= half_size; i++) {
float x = i / (float)half_size;
int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin();
float t;
if(index < cdf.size() - 1) {
t = (x - cdf[index])/(cdf[index+1] - cdf[index]);
} else {
t = 0.0f;
index = cdf.size() - 1;
}
float y = ((index + t) / (resolution - 1)) * (2.0f * range);
inv_cdf[half_size+i] = 0.5f*(1.0f + y);
inv_cdf[half_size-i] = 0.5f*(1.0f - y);
}
}
else {
for(int i = 0; i < resolution; i++) {
float x = from + range * (float)i * inv_resolution;
int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin();
float t;
if(index < cdf.size() - 1) {
t = (x - cdf[index])/(cdf[index+1] - cdf[index]);
} else {
t = 0.0f;
index = resolution;
}
inv_cdf[i] = (index + t) * inv_resolution;
}
}
}
CCL_NAMESPACE_END
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