neon

问题 in my project I'm making use of Eigen C++ library for linear algebra and ONLY when I turn on the vectorization flags (mfpu=neon -mfloat-abi=softfp) for ARM NEON, I get compiler errors. I'm not able to understand whats going wrong. Do I need to enable any preprocessor directives for ARM NEON in the Eigen Library? main.c #include<iostream> #include <Eigen/Core> // import most common Eigen types using namespace Eigen; int main(int, char *[]) { Matrix4f m3; m3 << 1, 2, 3, 0, 4, 5, 6, 0, 7, 8, 9,

问题 I have a code base which compiles fine in all other NEON compilers, ndk-build, RVDS, etc, but under Xcode I get the error "bad instruction" for every NEON instruction I call. It basically seems like NEON is not detected. I am attempting to build a static library, I went to New Project, selected Cocoa Touch Static Library, then added my existing files. Everything I'm reading indicates that NEON should be already enabled. I removed all references to armv6, and am targeting iOS 5.1 Also the code

问题 I'm trying to implement a row-by-row version of this image downscaling algorithm: http://intel.ly/1avllXm , applied to RGBA 8bit images. To simplify, consider resizing a single row, w_src -> w_dst. Then each pixel may contribute its value to a single output accumulator with weight 1.0, or contribute to two consecutive output pixels with weights alpha and (1.0f - alpha). In C/pseudo-code: float acc[w_dst] = malloc(w_dst * 4); x_dst = 0 for x = 0 .. w_src: if x is a pivot column: acc[x_dst] +=

问题 Hi I successfully built the appunite ffmpeg library including arm-v7a neon support, however when I try to run the libraries on my Marshmallow device I get this error: 01-08 23:42:02.350: E/AndroidRuntime(10144): java.lang.UnsatisfiedLinkError: dlopen failed: /data/app/com.example.demo-1/lib/arm/libffmpeg-neon.so: has text relocations When I use the non-neon builds it works without any problems. So I googled a bit and found out, that this is probably a bug in the corresponding C/C++ code but

问题 I wrote some neon code in assembly and was aiming for maximum optimization. Though the numbers seem satisfactory, I was interested in understanding the possibilities of optimizing it further. Then I came across an online tool which helps in counting the cycles of each instruction. Here goes the link to my code: http://pulsar.webshaker.net/ccc/sample-115d4c29 It clearly marked the areas of my concern, but I could not clearly understand the reason for those statements to contain the overheads.

问题 What is the difference between NEON SIMD and NEON SIMD version 2 as in Cortex A15? 回答1: It adds SIMD FMA instruction (VFMA.F32) and also mandates NEON half precision extension. NEONv2 is supported in ARM Cortex-A7, ARM Cortex-A15, and Qualcomm Krait (not sure about ARM Cortex-A5). 回答2: It is not that much of a difference, from ARM ARM: (in reverse order of definitions) Advanced SIMDv2 is an OPTIONAL extension to the ARMv7-A and ARMv7-R profiles. Advanced SIMDv2 adds both the Half-precision

问题 I have two tabs of floats. I need to multiply elements from the first tab by corresponding elements from the second tab and store the result in a third tab. I would like to use NEON to parallelize floats multiplications: four float multiplications simultaneously instead of one. I have expected significant acceleration but I achieved only about 20% execution time reduction. This is my code: #include <stdlib.h> #include <iostream> #include <arm_neon.h> const int n = 100; // table size /* fill a

问题 I recently discovered about the vreinterpret{q}_dsttype_srctype casting operator. However this doesn't seem to support conversion in the data type described at this link (bottom of the page): Some intrinsics use an array of vector types of the form: <type><size>x<number of lanes>x<length of array>_t These types are treated as ordinary C structures containing a single element named val. An example structure definition is: struct int16x4x2_t { int16x4_t val[2]; }; Do you know how to convert

问题 I'm working on a SIMD optimization of BGR to grayscale conversion which is equivalent to OpenCV's cvtColor() function. There is an Intel SSE version of this function and I'm referring to it. (What I'm doing is basically converting SSE code to NEON code.) I've almost finished writing the code, and can compile it with g++, but I can't get the proper output. Does anyone have any ideas what the error could be? What I'm getting (incorrect): What I should be getting: Here's my code: #include

问题 I'm trying to optimize an image format conversion on iOS using the NEON vector instruction set. I assumed this would map well to that because it processes a bunch of similar data. My attempts haven't gone that well, though, achieving only a marginal speedup vs the naive c implementation: for(int i = 0; i < pixelCount; ++i, ++inPixel32) { const unsigned int r = ((*inPixel32 >> 0 ) & 0xFF); const unsigned int g = ((*inPixel32 >> 8 ) & 0xFF); const unsigned int b = ((*inPixel32 >> 16) & 0xFF);