SQL Server stores the data on disk in set and fixed fashion. The order in sys.columns and key columns has no relevance to this on-disk order. See “Anatomy of a record” (Paul Randal) and my answer here: How do you get to limits of 8060 bytes per row and 8000 per (varchar, nvarchar) value?
Let’s do some tunning. Prime factorization of TimeSpan.TicksPerDay (864000000000) : DayOfWeek now can be expressed as: public DayOfWeek DayOfWeek { get { return (DayOfWeek)(((Ticks>>14) / 52734375 + 1L) % 7L); } } And we are working in modulo 7, 52734375 % 7 it’s 1. So, the code above is equal to: public static DayOfWeek dayOfWeekTurbo(this … Read more
using 1 char array could work a bit better int length = s.length(); char[] oldChars = new char[length]; s.getChars(0, length, oldChars, 0); int newLen = 0; for (int j = 0; j < length; j++) { char ch = oldChars[j]; if (ch >= ‘ ‘) { oldChars[newLen] = ch; newLen++; } } s = new … Read more
This should be possible at about 8 elements (1 AVX2 vector) per 2.5 clock cycles or so (per core) on a modern x86-64 like Skylake or Zen 2, using AVX2. Or per 2 clocks with unrolling. Or on your Piledriver CPU, maybe 1x 16-byte vector of indexes per 3 clocks with AVX1 _mm_cmpeq_epi32. The general … Read more
NOSPLIT: Similarly, NASM will split [eax*2] into [eax+eax] because that allows the offset field to be absent and space to be saved; in fact, it will also split [eax*2+offset] into [eax+eax+offset]. You can combat this behaviour by the use of the NOSPLIT keyword: [nosplit eax*2] will force [eax*2+0] to be generated literally. [nosplit eax*1] also … Read more
See also First use of AVX 256-bit vectors slows down 128-bit vector and AVX scalar ops re: implicit widening of 128-bit AVX operations to 256-bit if any uppers are dirty. (Including for the purposes of “light” vs. “heavy” turbo limits). This could be a reason to use vzeroupper, especially if you have some regions of … Read more
The best reference is the Intel Optimization Manual, which provides fairly detailed information on architectural hazards and instruction latencies for all recent Intel cores, as well as a good number of optimization examples. Another excellent reference is Agner Fog’s optimization resources, which have the virtue of also covering AMD cores. Note that specific cost models … Read more
Use the operation that best describes what you are trying to do. If you are treating the number as a sequence of bits, use bitshift. If you are treating it as a numerical value, use division. Note that they are not exactly equivalent. They can give different results for negative integers. For example: -5 / … Read more
It is not really a full answer, but still evidence that the penalty is visible. MSVC 2022 benchmark, compiler with /std:c++latest. #include <chrono> #include <iostream> struct alignas(16) S { char* a; int* b; }; extern “C” void init_fused_copy_unfused(int n, S & s2, S & s1); extern “C” void init_fused_copy_fused(int n, S & s2, S & … Read more