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5c84eca210
Since commit 07223c5c27 (Tutorial: Update Step 5 to work on Windows,
2020-02-18, v3.18.0-rc1~655^2) the logic does not work on non-Windows
platforms when cmake is re-run on an existing build tree. It is also
more complicated than we'd like for a tutorial example. Avoid the need
to consider the `m` library case by performing the check as C++.
Since `check_cxx_symbol_exists` cannot handle overloaded functions
like `exp` and `log`, check with `check_cxx_source_compiles` instead.
This also presents a more general-purpose example in the tutorial.
Fixes: #23524
33 lines
765 B
C++
33 lines
765 B
C++
#include <cmath>
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#include <iostream>
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#include "MathFunctions.h"
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// a hack square root calculation using simple operations
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double mysqrt(double x)
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{
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if (x <= 0) {
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return 0;
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}
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// if we have both log and exp then use them
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#if defined(HAVE_LOG) && defined(HAVE_EXP)
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double result = std::exp(std::log(x) * 0.5);
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std::cout << "Computing sqrt of " << x << " to be " << result
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<< " using log and exp" << std::endl;
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#else
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double result = x;
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// do ten iterations
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for (int i = 0; i < 10; ++i) {
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if (result <= 0) {
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result = 0.1;
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}
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double delta = x - (result * result);
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result = result + 0.5 * delta / result;
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std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
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}
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#endif
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return result;
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}
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