testcode.git

Add two implementations of round_up_to_next_power_of_two
Parent 632a848
David Blume

David Blume commited on 2019-01-24 20:54:16
Showing 5 changed files, with 82 additions and 4 deletions.

.gitignore
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@@ -1 +1 @@
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-*.exe
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+testcode
product/Makefile
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@@ -6,7 +6,8 @@ LDFLAGS=-pthread -L $(LIBDIR) -lmy_lib
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 OBJDIR=obj
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 SOURCES=main.cpp main_helper.cpp ui/widget.cpp scoped_set_adder.cpp \
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-	thread_with_lambda.cpp thread_manager.cpp deadlock/deadlock.cpp
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+	thread_with_lambda.cpp thread_manager.cpp deadlock/deadlock.cpp \
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+	next_power_of_two
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 # //OBJECTS=$(OBJDIR)$(SOURCES:.cpp=.o)
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 OBJECTS=$(foreach bname, $(basename $(SOURCES)), $(OBJDIR)/$(bname).o)
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 EXECUTABLE=testcode
product/main.cpp
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@@ -5,6 +5,7 @@
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 #include <algorithm>
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 #include <memory>
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 #include <complex>
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+#include <cassert>
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 #include "main_helper.hpp"
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 #include "scoped_set_adder.hpp"
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 #include "ui/widget.hpp"
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@@ -12,6 +13,7 @@
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 #include "thread_with_lambda.hpp"
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 #include "thread_manager.hpp"
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 #include "deadlock/deadlock.hpp"
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+#include "next_power_of_two.hpp"
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 using namespace std;
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 using namespace MY_LIB;
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@@ -71,6 +73,16 @@ void test_cpp14() {
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 #endif
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 }
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+struct Base {
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+    virtual ~Base() {}
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+    virtual void f() {}
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+    int x_;
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+};
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+
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+struct Derived: Base {
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+    virtual void name() {}
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+};
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+
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 int main() {
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     length_of_array = 6;
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     int a[6] = { 10, 20, 20, 30, 40, 40 };
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@@ -78,6 +90,18 @@ int main() {
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     // thread_with_lambda();
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+    Base * pb = new Derived;
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+    std::shared_ptr<Base> sp(pb);
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+    cout << "pb is " << pb << endl;
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+    cout << "sp is " << sp << endl;
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+    Derived * pd = dynamic_cast<Derived *>(sp.get());
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+    if (pd) {
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+        cout << "pd exists " << endl;
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+    } else {
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+        cout << "pd is NULL " << endl;
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+    }
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+    cout << "pd is " << pd << endl;
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+
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     cout << "Removing " << item_to_remove << endl;
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     length_of_array = remove_element(a, length_of_array, item_to_remove);
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     cout << "a became " << a << endl;
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@@ -128,8 +152,10 @@ int main() {
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     // cout << "deadlock() returned " << deadlock() << endl;
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-    // This_function_is_not_defined();
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-
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+    for(unsigned i : {0, 1, 2, 3, 4, 5, 6, 7, 31, 32, 33, 4003, 65535, 65536, 65537}) {
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+        cout << "next_power_of_two(" << i << ") = " << round_up_to_next_power_of_two(i) << endl;
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+        assert(round_up_to_next_power_of_two(i) == another_round_up_to_next_power_of_two(i));
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+    }
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     cout << "Done." << endl;
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     return 0;
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 }
product/next_power_of_two.cpp
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@@ -0,0 +1,24 @@
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+#include <climits>
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+#include "next_power_of_two.hpp"
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+
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+using namespace std;
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+
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+#ifndef USE_TEMPLATE
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+
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+unsigned round_up_to_next_power_of_two(unsigned x)
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+{
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+    // https://stackoverflow.com/questions/466204/rounding-up-to-next-power-of-2
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+    --x;
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+    for(size_t i = 1; i < sizeof(x) * CHAR_BIT; i *= 2)
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+        x |= x >> i;
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+    return ++x;
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+}
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+
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+#endif
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+
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+unsigned another_round_up_to_next_power_of_two(unsigned x)
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+{
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+    // https://stackoverflow.com/questions/671815/what-is-the-fastest-most-efficient-way-to-find-the-highest-set-bit-msb-in-an-i
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+    return (x > 1) ? 1 << (sizeof(x) * CHAR_BIT - __builtin_clz(x-1)) : x;
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+}
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+
product/next_power_of_two.hpp
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@@ -0,0 +1,27 @@
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+#pragma once
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+
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+#define USE_TEMPLATE
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+#ifdef USE_TEMPLATE
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+
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+#include <cstddef>
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+#include <type_traits>
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+#include <climits>
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+
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+template <typename T>
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+T round_up_to_next_power_of_two(T x)
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+{
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+    // https://stackoverflow.com/questions/466204/rounding-up-to-next-power-of-2
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+     static_assert(std::is_unsigned<T>::value, "x must be an unsigned type");
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+    --x;
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+    for(size_t i = 1; i < sizeof(x) * CHAR_BIT; i *= 2)
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+        x |= x >> i;
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+    return ++x;
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+}
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+
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+#else
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+
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+unsigned round_up_to_next_power_of_two(unsigned x);
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+
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+#endif
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+
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+unsigned another_round_up_to_next_power_of_two(unsigned x);
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