Dijkstra derives an eloquent solution in “A Discipline of Programming”. He attributes the problem to Hamming. Here is my implementation of Dijkstra’s solution. int main() { const int n = 20; // Generate the first n numbers std::vector<int> v(n); v[0] = 1; int i2 = 0; // Index for 2 int i5 = 0; // … Read more
This is an interesting problem. Taking it by the book, you can start off with this: %PDF-1.0 1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj 2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj 3 0 obj<</Type/Page/MediaBox[0 0 3 3]>>endobj xref 0 4 0000000000 65535 f 0000000010 00000 n 0000000053 00000 n 0000000102 00000 n trailer<</Size 4/Root 1 0 R>> … Read more
My experience with larger files sizes has been that java.nio is faster than java.io. Solidly faster. Like in the >250% range. That said, I am eliminating obvious bottlenecks, which I suggest your micro-benchmark might suffer from. Potential areas for investigating: The buffer size. The algorithm you basically have is copy from disk to buffer copy … Read more
I was going to write up my own explanation but this Wikipedia article pretty much sums it up. Here is the basic concept: Copy-on-write (sometimes referred to as “COW”) is an optimization strategy used in computer programming. The fundamental idea is that if multiple callers ask for resources which are initially indistinguishable, you can give … Read more
Proof: a=”foo” a.object_id #=> 2154889340 a << ‘bar’ a.object_id #=> 2154889340 a += ‘quux’ a.object_id #=> 2154742560 So << alters the original string rather than creating a new one. The reason for this is that in ruby a += b is syntactic shorthand for a = a + b (the same goes for the other … Read more
Yes, it is possible. For example, for gcc you can use __builtin_unreachable to tell the compiler about impossible conditions, like so: if (value < 0 || value > 36) __builtin_unreachable(); We can wrap the condition above in a macro: #define assume(cond) do { if (!(cond)) __builtin_unreachable(); } while (0) And use it like so: assume(x … Read more
Use switch. In the worst case the compiler will generate the same code as a if-else chain, so you don’t lose anything. If in doubt put the most common cases first into the switch statement. In the best case the optimizer may find a better way to generate the code. Common things a compiler does … Read more
It’s not faster. If you really care, compile with assembler output for your platform and look to see. It doesn’t matter. This never matters. Write your infinite loops however you like.
Background / Overview Operations on automatic variables (“from the stack”, which are variables that you create without calling malloc / new) are generally much faster than those involving the free store (“the heap”, which are variables that are created using new). However, the size of automatic arrays is fixed at compile time, but the size … Read more
The reason is that lambdas are function objects so passing them to a function template will instantiate a new function specifically for that object. The compiler can thus trivially inline the lambda call. For functions, on the other hand, the old caveat applies: a function pointer gets passed to the function template, and compilers traditionally … Read more