neon

How could NEON be as slow as C? I have been trying to build a fast Histogram function that would bucket incoming values into ranges by assigning them a value - which is the range threshold they are closest to. This is something that would be applied to images so it would have to be fast (assume an image array of 640x480 so 300,000 elements) . The histogram range numbers are multiples (0,25,50,75,100) . Inputs would be float and final outputs would obviously be integers I tested the following versions on xCode by opening a new empty project (no app delegate) and just using the main.m file. I

Does there exist an approach for calculating the determinant of matrices with low dimensions (about 4), that works well with SIMD (neon, SSE, SSE2)? I am using a hand-expansion formula, which does not work so well. I am using SSE all the way to SSE3 and neon, both under linux. The matrix elements are all floats. Here's my 5 cents. determinant of a 2x2 matrix: that's an exercise for the reader, should be simple to implement determinant of a 3x3 matrix: use the scalar triple product. This will require smart cross() and dot() implementations. The recipes for these are widely available.

How do I find max element in array of 8 bytes, 8 shorts or 8 ints? I may need just the position of the max element, value of the max element, or both of them. For example : unsigned FindMax8(const uint32_t src[8]) // returns position of max element { unsigned ret = 0; for (unsigned i=0; i<8; ++i) { if (src[i] > src[ret]) ret = i; } return ret; } At -O2 clang unrolls the loop but it does not use neon, which should give decent perf boost (because it eliminates many data dependent branches?) For 8 bytes and 8 shorts approach should be simpler as entire array can be loaded into a single q-register

I'm trying to call a function that is coded in ARM NEON assembly in an .s file that looks like this: AREA myfunction, code, readonly, ARM global fun align 4 fun push {r4, r5, r6, r7, lr} add r7, sp, #12 push {r8, r10, r11} sub r4, sp, #64 bic r4, r4, #15 mov sp, r4 vst1.64 {d8, d9, d10, d11}, [r4]! vst1.64 {d12, d13, d14, d15}, [r4] [....] and I'm assembling it like this: armasm.exe -32 func.s func.obj Unfortunately this doesn't work, and I'm getting illegal instruction exception when I try and call the function. When I used dumpbin.exe to disassemble the .obj, it seem to be disassembling as

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Im rather new to assembly and although the arm information center is often helpful sometimes the instructions can be a little confusing to a newbie. Basically what I need to do is sum 4 float values in a quadword register and store the result in a single precision register. I think the instruction VPADD can do what I need but I'm not quite sure. It seems that you want to get the sum of a certain length of array, and not only four float values. In that case, your code will work, but is far from optimized : many many pipeline interlocks unnecessary 32bit addition per iteration Assuming the

I want to use Neon SIMD instruction for the iphone. I heard we have to put flags "-mfloat-abi=softfp -mfpu=neon" in the "Other C Flags" field of the Target inspector, but when building I get "error: unrecognized command line option "-mfpu=neon"" . Is there anything else special that has to be done to allow this flag? (I have Xcode 3.2.1 and iphone sdk 3.1.3) Thanks !! The NEON set is an extension on the Cortex-A series, therefore not supported in iPhone 3G. You probably cannot specify this directly. NEON is enabled by default. The target has to be ARMv7 for that. (3GS or later) In order to