Shader Model 6.4

Packed Dot Product Intrinsics

The new shader model adds the following 3 intrinsics to accelerate dot products on reduced precision data:

Unsigned Integer Dot-Product of 4 Elements and Accumulate:

uint32 dot4add_u8packed( uint32 a, uint32 b, uint32 acc ); // ubyte4 a, b;

 A 4-dimensional unsigned integer dot-product with add. Multiplies together each corresponding pair of unsigned 8-bit int bytes in the two input DWORDs, and sums the results into the 32-bit unsigned integer accumulator. This instruction operates within a single 32-bit wide SIMD lane. The inputs are also assumed to be 32-bit quantities.

Signed Integer Dot-Product of 4 Elements and Accumulate:

int32  dot4add_i8packed( uint32 a, uint32 b,  int32 acc );          // signed byte4 a, b;

 A 4-dimensional signed integer dot-product with add. Multiplies together each corresponding pair of signed 8-bit int bytes in the two input DWORDs, and sums the results into the 32-bit signed integer accumulator. This instruction operates within a single 32-bit wide SIMD lane. The inputs are also assumed to be 32-bit quantities.

Single Precision Floating Point 2-Element Dot-Product and Accumulate:

float dot2add( half2 a, half2 b, float acc );

 A 2-dimensional floating point dot product of half2 vectors with add. Multiplies the elements of the two half-precision float input vectors together and sums the results into the 32-bit float accumulator. These instructions operate within a single 32-bit wide SIMD lane. The inputs are 16-bit quantities packed into the same lane. This is not considered a ‘fused’ operation, and so need not emit INF due to fp16 overflow unless the precise declaration is used.

This covered under the low-precision feature bit (indicating native half and short support).

Support for Variable Rate Shading

Variable rate shading is supported as of this shader model. Only one token was added to HLSL.

SV_ShadingRate

Indicates the number of samples per pixel during operation of the current pixel shader thread.

See the variable rate shading spec for more details.

Library Sub-objects

Check the developer documentation on DirectX raytracing here