Being consistent is the most important thing; If I’m working on existing code that already has LSE-first comments or variable names, I match that. Given the choice, I prefer MSE-first notation in comments, especially when designing something with shuffles or especially packing/unpacking to different element sizes. Intel uses MSE-first not only in their diagrams in … Read more
You can’t vpinsrq into a YMM register. Only an xmm destination is available, so it unavoidably zeros the upper lane of the full YMM register. It was introduced with AVX1 as the VEX version of the 128-bit instruction. AVX2 and AVX512 did not upgrade it to YMM/ZMM destinations. I’m guessing they didn’t want to provide … Read more
Most compilers will automatically define: __SSE__ __SSE2__ __SSE3__ __AVX__ __AVX2__ etc, according to whatever command line switches you are passing. You can easily check this with gcc (or gcc-compatible compilers such as clang), like this: $ gcc -msse3 -dM -E – < /dev/null | egrep “SSE|AVX” | sort #define __SSE__ 1 #define __SSE2__ 1 #define … Read more
SSE is fully specified*. Muller is an expert in floating point arithmetic; who are you going to trust, him or some guy on a gamedev forum? (*) there are actually a few exceptions for non-IEEE-754 operations like rsqrtss, where Intel never fully specified the behavior, but that doesn’t effect the IEEE-754 basic operations, and more … Read more
The upcoming Mono 2.2 release will have SIMD support. Miguel de Icaza blogged about the upcoming feature here, and the API is here. Although there will be a library that will support development under Microsoft’s .NET Windows runtime, it will not have the performance benefits that you are looking for unless you run the code … Read more
From the file gcc/config/i386/i386.c of the GCC sources: b — print the QImode name of the register for the indicated operand. %b0 would print %al if operands[0] is reg 0. w — likewise, print the HImode name of the register. k — likewise, print the SImode name of the register. q — likewise, print the … Read more
Here are some codes I used in an old project (there is a research paper about it). The function popcnt8 below computes the number of bits set in each byte. SSE2-only version (based on Algorithm 3 in Hacker’s Delight book): static const __m128i popcount_mask1 = _mm_set1_epi8(0x77); static const __m128i popcount_mask2 = _mm_set1_epi8(0x0F); static inline __m128i … Read more
You can abuse PSADBW to calculate horizontal sums of bytes without overflow. For example: pxor xmm0, xmm0 psadbw xmm0, [a + 0] ; sum in 2x 64-bit chunks pxor xmm1, xmm1 psadbw xmm1, [a + 16] paddw xmm0, xmm1 ; accumulate vertically pshufd xmm1, xmm0, 2 ; bring down the high half paddw xmm0, xmm1 … Read more
These days you should normally just include <immintrin.h>. It includes everything. GCC and clang will stop you from using intrinsics for instructions you haven’t enabled at compile time (e.g. with -march=native or -mavx2 -mbmi2 -mpopcnt -mfma -mcx16 -mtune=znver1 or whatever.) MSVC and ICC will let you use intrinsics without enabling anything at compile time, but … Read more
There are lots of examples of the algorithm in practice. For example: Newton Raphson with SSE2 – can someone explain me these 3 lines has an answer explaining the iteration used by one of Intel’s examples. For perf analysis on let’s say Haswell (which can FP mul on two execution ports, unlike previous designs), I’ll … Read more