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92 lines
3.1 KiB
92 lines
3.1 KiB
/* |
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This file is part of Magnum. |
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Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, |
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2020 Vladimír Vondruš <mosra@centrum.cz> |
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Copyright © 2020 janos <janos.meny@googlemail.com> |
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Permission is hereby granted, free of charge, to any person obtaining a |
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copy of this software and associated documentation files (the "Software"), |
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to deal in the Software without restriction, including without limitation |
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the rights to use, copy, modify, merge, publish, distribute, sublicense, |
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and/or sell copies of the Software, and to permit persons to whom the |
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Software is furnished to do so, subject to the following conditions: |
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The above copyright notice and this permission notice shall be included |
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in all copies or substantial portions of the Software. |
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
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THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
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FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER |
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DEALINGS IN THE SOFTWARE. |
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*/ |
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#include <Corrade/Utility/Assert.h> |
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#include "Functions.h" |
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namespace Magnum { namespace Math { |
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#if !defined(CORRADE_TARGET_GCC) && !defined(CORRADE_TARGET_CLANG) |
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namespace { |
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/* https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel |
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there's also https://stackoverflow.com/a/109025 which mostly just copies |
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parts of this together with a lot of noise and syntax errors. */ |
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template<class T> inline UnsignedInt popcountImplementation(T v) { |
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v = v - ((v >> 1) & ~T(0)/3); |
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v = (v & ~T(0)/15*3) + ((v >> 2) & ~T(0)/15*3); |
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v = (v + (v >> 4)) & ~T(0)/255*15; |
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return (v*(~T(0)/255)) >> (sizeof(T) - 1)*8; |
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} |
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} |
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UnsignedInt popcount(UnsignedInt number) { |
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return popcountImplementation(number); |
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} |
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UnsignedInt popcount(UnsignedLong number) { |
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return popcountImplementation(number); |
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} |
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#endif |
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UnsignedInt log(UnsignedInt base, UnsignedInt number) { |
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UnsignedInt log = 0; |
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while(number /= base) |
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++log; |
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return log; |
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} |
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UnsignedInt log2(UnsignedInt number) { |
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UnsignedInt log = 0; |
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while(number >>= 1) |
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++log; |
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return log; |
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} |
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UnsignedLong binomialCoefficient(const UnsignedInt n, UnsignedInt k) { |
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CORRADE_ASSERT(n >= k, |
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"Math::binomialCoefficient(): k can't be greater than n in (" << Corrade::Utility::Debug::nospace << n << "choose" << k << Corrade::Utility::Debug::nospace << ")", {}); |
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/* k and n - k gives the same value, optimize the calculation to do fewer |
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steps */ |
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if(k*2 > n) k = n - k; |
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if(k == 0) return 1; |
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UnsignedLong result = n; |
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for(UnsignedInt i = 2; i <= k; ++i) { |
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CORRADE_ASSERT(result < ~UnsignedLong{} / (n-i+1), "Math::binomialCoefficient(): overflow for (" << Corrade::Utility::Debug::nospace << n << "choose" << k << Corrade::Utility::Debug::nospace << ")", {}); |
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result *= n - i + 1; |
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result /= i; |
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} |
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return result; |
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} |
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}}
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