hi, guys:
let me set an example:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int table[256]={......};
int lookup_tbl(int index)
{
return table[index];
}
int main()
int idx0, idx1, idx2, idx3;
int tbl0, tbl1, tbl2, tbl3;
idx0 = 2;
idx1 = 36;
idx2 = 111;
idx3 = 204;
tbl0 = lookup_tbl(idx0);
tbl1 = lookup_tbl(idx1);
tbl2 = lookup_tbl(idx2);
tbl3 = lookup_tbl(idx3);
my question is:
Could I use some neon intrinsic(maybe VTBL) to get the 4 values once? if I have set the index into a 32x4_t variable ?
thank you very much.
Hi,
Yes, NEON instructions can be useful for loading multiple values at once but they can't be used to achieve what you are trying to do. From what I can see, you are trying to load four essentially arbitrary elements from an array (in your example, elements 2, 36, 111 and 204). NEON load instructions can load 4 32-bit values in a single operation but they have to be contiguous elements (there are some variations here which use the structured load instructions to de-interleave structured data but they still operate on contiguous elements in memory).
For instance:
int32x4_t temp;
temp = vld1q_s32(table);
compiles to:
LDR r0, =table
VLD1.32 {d0,d1}, [r0]
This loads 4 consecutive 32-bit words from the table. But I'm afraid they do have to be consecutive.
Chris