simd

问题 Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . Improve this question I'm looking into using these to improve the performance of some code but good documentation seems hard to find for the functions defined in the *mmintrin.h headers, can anybody provide me with pointers to good info on these? EDIT: particularly interested in a very

问题 I'm trying to use SSE intrinsics to add two 32-bit signed int arrays. But I'm getting very poor performance compared to a linear addition. Platform - Intel Core i3 550, GCC 4.4.3, Ubuntu 10.04 (bit old, yeah) #define ITER 1000 typedef union sint4_u { __m128i v; sint32_t x[4]; } sint4; The functions: void compute(sint32_t *a, sint32_t *b, sint32_t *c) { sint32_t len = 96000; sint32_t i, j; __m128i x __attribute__ ((aligned(16))); __m128i y __attribute__ ((aligned(16))); sint4 z; for(j = 0; j <

问题 AVX allow for bitwise logical operations such as and/or on floating point data-type __m256 and __m256d. However, C++ doesn't allow for bitwise operations on floats and doubles, reasonably. If I'm right, there's no guarantee on the internal representation of floats, whether the compiler will use IEEE754 or not, hence a programmer can't be sure about how the bits of a float will look like. Consider this example: #include <immintrin.h> #include <iostream> #include <limits> #include <cassert> int

问题 I see people using -msse -msse2 -mfpmath=sse flags by default hoping that this will improve performance. I know that SSE gets engaged when special vector types are used in the C code. But do these flags make any difference for regular C code? Does compiler use SSE to optimize regular C code? 回答1: Yes, modern compilers auto-vectorize with SSE2 if you compile with full optimization. clang enables it even at -O2, gcc at -O3. Even at -O1 or -Os, compilers will use SIMD load/store instructions to

问题 I'm on the Intel Intrinsic site and I can't figure out what combination of instructions I want. What I'd like to do is result = high_table[i8>>4] & low_table[i8&15] Where both table are 16bits (or more). shuffle seems like what I want (_mm_shuffle_epi8) however getting a 8bit value doesn't work for me. There doesn't seem to be a 16bit version and the non byte version seems to need the second param as an immediate value. How am I suppose to implement this? Do I call _mm_shuffle_epi8 twice for

问题 I'm trying to use the Java Vector API from the Panama project to add some SIMD code to the java.math.BigInteger class. I cloned the Panama repo and built a JDK: hg clone http://hg.openjdk.java.net/panama/dev/ cd dev/ hg checkout vectorIntrinsics hg branch vectorIntrinsics bash configure make images I was able to compile and run a simple little program that uses the vector API: import static jdk.incubator.vector.Vector.Shape.S_256_BIT; import jdk.incubator.vector.IntVector; import static jdk

问题 I'm trying to use the Java Vector API from the Panama project to add some SIMD code to the java.math.BigInteger class. I cloned the Panama repo and built a JDK: hg clone http://hg.openjdk.java.net/panama/dev/ cd dev/ hg checkout vectorIntrinsics hg branch vectorIntrinsics bash configure make images I was able to compile and run a simple little program that uses the vector API: import static jdk.incubator.vector.Vector.Shape.S_256_BIT; import jdk.incubator.vector.IntVector; import static jdk

问题 When using SSE2 instructions such as PADDD (i.e., the _mm_add_epi32 intrinsic), is there a way to check whether any of the operations overflowed? I thought that maybe a flag on the MXCSR control register may get set after an overflow, but I don't see that happening. For example, _mm_getcsr() prints the same value in both cases below (8064): #include <iostream> #include <emmintrin.h> using namespace std; void main() { __m128i a = _mm_set_epi32(1, 0, 0, 0); __m128i b = _mm_add_epi32(a, a); cout

问题 When using SSE2 instructions such as PADDD (i.e., the _mm_add_epi32 intrinsic), is there a way to check whether any of the operations overflowed? I thought that maybe a flag on the MXCSR control register may get set after an overflow, but I don't see that happening. For example, _mm_getcsr() prints the same value in both cases below (8064): #include <iostream> #include <emmintrin.h> using namespace std; void main() { __m128i a = _mm_set_epi32(1, 0, 0, 0); __m128i b = _mm_add_epi32(a, a); cout

问题 I have written a library, where I use CMake for verifying the presence of headers for MMX, SSE, SSE2, SSE4, AVX, AVX2, and AVX-512. In addition to this, I check for the presence of the instructions and if present, I add the necessary compiler flags, -msse2 -mavx -mfma etc. This is all very good, but I would like to deploy a single binary, which works across a range of generations of processors. Question: Is it possible to tell the compiler (GCC) that whenever it optimizes a function using