AMD 250 manual Additional Considerations, Instead, use the equivalent array notation

Software Optimization Guide for AMD64 Processors 25112 Rev. 3.06 September 2005

Instead, use the equivalent array notation:

typedef struct { float x, y, z, w;

} VERTEX;

typedef struct { float m[4][4];

} MATRIX;

void XForm(float *res, const float *v, const float *m, int numverts) {

int i;

const VERTEX* vv = (VERTEX *)v; const MATRIX* mm = (MATRIX *)m; VERTEX* rr = (VERTEX *)res;

for (i =	0; i < numverts; i++) {
rr->x	= vv->x * mm->m[0][0] + vv->y * mm->m[0][1] +
	vv->z * mm->m[0][2] + vv->w * mm->m[0][3];
rr->y	= vv->x * mm->m[1][0] + vv->y * mm->m[1][1] +
	vv->z * mm->m[1][2] + vv->w * mm->m[1][3];
rr->z	= vv->x * mm->m[2][0] + vv->y * mm->m[2][1] +
	vv->z * mm->m[2][2] + vv->w * mm->m[2][3];
rr->w	= vv->x * mm->m[3][0] + vv->y * mm->m[3][1] +
	vv->z * mm->m[3][2] + vv->w * mm->m[3][3];
++rr;	// Increment the results pointer.
++vv;	// Increment the input vertex pointer.
}

}

Additional Considerations

Source-code transformations interact with a compiler’s code generator, making it difficult to control the generated machine code from the source level. It is even possible that source-code transformations aimed at improving performance may conflict with compiler optimizations. Depending on the compiler and the specific source code, it is possible for pointer-style code to compile into machine code that is faster than that generated from equivalent array-style code. Compare the performance of your code after implementing a source-code transformation with the performance of the original code to be sure that there is an improvement.

12 C and C++ Source-Level Optimizations Chapter 2