WavePrefixProduct function
Returns the product of all of the values in the active lanes in this wave with indices less than this lane.
Syntax
<type> WavePrefixProduct(
<type> value
);
Parameters
value
The value to multiply.
Return value
The product of all the values.
Remarks
The order of operations on this routine cannot be guaranteed. So, effectively, the [precise] flag is ignored within it.
A postfix product can be computed by multiplying the prefix product by the current lane's value.
Note that the active lane with the lowest index will always receive a 1 for its prefix product.
This function is supported from shader model 6.0 in all shader stages.
Examples
uint numToMultiply = 2;
uint prefixProduct = WavePrefixProduct( numToMultiply );
On a machine with a wave size of 8, and all lanes active except lanes 0 and 4, the following values would be returned from WavePrefixProduct.
| lane index | status | prefixProduct |
|---|---|---|
| 0 | inactive | n/a |
| 1 | active | = 1 |
| 2 | active | = 1*2 |
| 3 | active | = 1*2*2 |
| 4 | inactive | n/a |
| 5 | active | = 1*2*2*2 |
| 6 | active | = 1*2*2*2*2 |
| 7 | active | = 1*2*2*2*2*2 |