85 lines
1.3 KiB
C++
85 lines
1.3 KiB
C++
#ifndef KAHANSUM_H
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#define KAHANSUM_H
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#include <vector>
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template <typename T> class KahanSum {
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private:
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const T zero;
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/** current sum */
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T sum;
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/** current compensation */
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T comp;
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public:
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/** ctor with zero element */
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KahanSum(const T zero) : zero(zero), sum(zero), comp(zero) {
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}
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KahanSum& operator += (const T val) {
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add(val);
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return *this;
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}
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KahanSum& operator -= (const T val) {
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sub(val);
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return *this;
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}
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T get() const {
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return sum;
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}
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private:
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#define NO_OPT __attribute__((optimize("-O0")))
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/** adjust the sum */
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void add(const T val) NO_OPT {
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const T y = val - comp;
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const T t = sum + y;
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comp = (t-sum) - y; // very important line
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sum = t;
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}
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/** adjust the sum */
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void sub(const T val) NO_OPT {
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const T y = val - comp;
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const T t = sum - y;
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comp = (t-sum) + y; // very important line
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sum = t;
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}
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public:
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static T get(const std::vector<T>& values, const T zero = T()) {
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return get(values.data(), values.size(), zero);
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}
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static T get(const T* values, const size_t cnt, const T zero = T()) {
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T sum = zero;
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volatile T comp = zero;
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for (size_t i = 0; i < cnt; ++i) {
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const T inp = values[i];
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const volatile T y = inp - comp;
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const volatile T t = sum + y;
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comp = (t-sum) - y;
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sum = t;
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}
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return sum;
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}
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};
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#endif // KAHANSUM_H
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