• Locked Locked
  • Replies 2 replies
  • Subscribers 119 subscribers
  • Views 3089 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

NEON matrix multiply

John Doe
Note: This was originally posted on 24th November 2011 at http://forums.arm.com

I'm new to neon and I'm trying to do some multiplication.
I need to do some multiplication of two arrays and I'm trying to learn some NEON assembly.

I have 2 arrays of int16_t elements. Each array has 4 elements (a[0]-a[3] and b[0]-b[3])
I need to produce resulting array c with 4 int16_t values as:

c[0] = a[0] * b[0]
c[1] = a[0] * b[1] + a[1] * b[1]
c[2] = a[0] * b[2] + a[1] * b[2] + a[2] * b[2]
c[3] = a[0] * b[3] + a[1] * b[3] + a[2] * b[3] + a[3] * b[3]

I'm sure that something like that should be trivial in NEON but I have no idea how to get it working.

My approach is like this:

vmov.32   d0, #0  // (destination array c)
//load arrays a and b into d1 and d2:
vld1.16  d1, [r0]
vld1.16  d2, [r1]

vmla.s16 d0, d1, d2[0]   // 1st column
// ? TODO... rotate
vmla.s16 d0, d1, d2[1]   // 2nd column
vmla.s16 d0, d1, d2[2]
vmla.s16 d0, d1, d2[3]



Basically, at the place of my TODO I want to shift elements of array b so that b becomes:  {b[0], b[1], b[2], b[3]} -> {0, b[0], b[1], b[2]}


Is my approach correct, or I cannot do so in arm-neon?
PS. I tried to use intrinsics with evaluation version of RVDS and it seems that it doesn't work: the generated asm is empty and doesn't have these instructions at all!


Thanks.