57
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15
answers
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Quickly find whether a value is present in a C array?
I have an embedded application with a time-critical ISR that needs to iterate through an array of size 256 (pr
53
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1
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1K
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What is the best way to set a register to zero in x86 assembly: xor, mov or and?
All the following instructions do the same thing: set %eax to zero. Which way is optimal (requiring fewest mac
50
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3
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Why does GCC generate such radically different assembly for nearly the same C code?
While writing an optimized ftol function I found some very odd behaviour in GCC 4.6.1. Let me show you the cod
56
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4
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Why would introducing useless MOV instructions speed up a tight loop in x86_64 assembly?
Background: While optimizing some Pascal code with embedded assembly language, I noticed an unnecessary MOV i
58
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11
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1.9K
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Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly?
I wrote these two solutions for Project Euler Q14, in assembly and in C++. They implement identical brute forc
64
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11
answers
1.9K
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Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
I was looking for the fastest way to popcount large arrays of data. I encountered a very weird effect: Changin
58
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12
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935
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Why doesn't GCC optimize a*a*a*a*a*a to (a*a*a)*(a*a*a)?
I am doing some numerical optimization on a scientific application. One thing I noticed is that GCC will optim
67
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30
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Fastest way to list all primes below N
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55
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30
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Fastest way to determine if an integer's square root is an integer
I'm looking for the fastest way to determine if a long value is a perfect square (i.e. its square root is
51
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9
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Swift Beta performance: sorting arrays
I was implementing an algorithm in Swift Beta and noticed that the performance was very poor. After digging de
61
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30
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Which "href" value should I use for JavaScript links, "#" or "javascript:void(0)"?
The following are two methods of building a link that has the sole purpose of running JavaScript code. Which i
