Intel® 64 and IA-32 Architectures Optimization Reference Manual

CODING FOR SIMD ARCHITECTURESExample 4-12. AoS Data Structuretypedef struct{float x,y,z;int a,b,c;. . .} Vertex;Vertex Vertices[NumOfVertices];The best processing method for code using SIMD technology is to arrange the data inan array for each coordinate (Example 4-13). This data arrangement is called structureof arrays (SoA).Example 4-13. SoA Data Structuretypedef struct{float x[NumOfVertices];float y[NumOfVertices];float z[NumOfVertices];int a[NumOfVertices];int b[NumOfVertices];int c[NumOfVertices];. . .} VerticesList;VerticesList Vertices;There are two options for computing data in AoS format: perform operation on thedata as it stands in AoS format, or re-arrange it (swizzle it) into SoA format dynamically.See Example 4-14 for code samples of each option based on a dot-productcomputation.Example 4-14. AoS and SoA Code Samples; The dot product of an array of vectors (Array) and a fixed vector (Fixed) is a; common operation in 3D lighting operations, where Array = (x0,y0,z0),(x1,y1,z1),...; and Fixed = (xF,yF,zF); A dot product is defined as the scalar quantity d0 = x0*xF + y0*yF + z0*zF.;; AoS code; All values marked DC are “don’t-care.”4-19