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Chapter 2 C and C++ Source-Level Optimizations 11
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
Example
Avoid code, such as the following, which uses pointer 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) {
float dp;
int i;
const VERTEX* vv = (VERTEX *)v;
for (i = 0; i < numverts; i++) {
dp = vv->x * *m++;
dp += vv->y * *m++;
dp += vv->z * *m++;
dp += vv->w * *m++;
*res++ = dp; // Write transformed x.
dp = vv->x * *m++;
dp += vv->y * *m++;
dp += vv->z * *m++;
dp += vv->w * *m++;
*res++ = dp; // Write transformed y.
dp = vv->x * *m++;
dp += vv->y * *m++;
dp += vv->z * *m++;
dp += vv->w * *m++;
*res++ = dp; // Write transformed z.
dp = vv->x * *m++;
dp += vv->y * *m++;
dp += vv->z * *m++;
dp += vv->w * *m++;
*res++ = dp; // Write transformed w.
++vv; // Next input vertex
m -= 16; // Reset to start of transform matrix.
}
}