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// ref: https://stackoverflow.com/questions/74382366/why-is-iterating-over-stdrangesviewsjoin-so-slow
#define NDEBUG
#include <stc/cspan.h>
#include <stdio.h>
#include <time.h>
using_cspan3(MD, double);
// define the dimensions of a 3d-array
enum {
nx = 64,
ny = 64,
nz = 64
};
// subspan 15x5x10:
int lx = 15, ly = 10, lz = 5;
int hx = 30, hy = 15, hz = 15;
// define the contents of two nx x ny x nz arrays in and out
double Vout[nx * ny * nz];
double Vin[nx * ny * nz]; //, 1.23;
// define some slice indices for each dimension
static void Traditional_for_loop(intptr_t n)
{
clock_t t = clock();
double sum = 0;
for (int s = 0; s < n; ++s) {
for (int x = lx; x < hx; ++x) {
for (int y = ly; y < hy; ++y) {
for (int z = lz; z < hz; ++z) {
double d = Vin[nz*(ny*x + y) + z];
Vout[nz*(ny*x + y) + z] += d;
sum += d;
}
}
}
}
t = clock() - t;
printf("forloop : %.1f ms, %f\n", 1000.0f*t / CLOCKS_PER_SEC, sum);
}
static void MDRanges_loop_over_joined(intptr_t n)
{
clock_t t = clock();
MD3 r_in = cspan_md(Vin, nx, ny, nz);
MD3 r_out = cspan_md(Vout, nx, ny, nz);
r_in = cspan_slice(MD3, &r_in, {lx, hx}, {ly, hy}, {lz, hz});
r_out = cspan_slice(MD3, &r_out, {lx, hx}, {ly, hy}, {lz, hz});
double sum = 0;
for (intptr_t s = 0; s < n; ++s) {
MD3_iter i = MD3_begin(&r_in);
MD3_iter o = MD3_begin(&r_out);
for (; i.ref; MD3_next(&i), MD3_next(&o))
{
*o.ref += *i.ref;
sum += *i.ref;
}
}
t = clock() - t;
printf("joined : %.1f ms, %f\n", 1000.0f*t / CLOCKS_PER_SEC, sum);
}
static void MDRanges_nested_loop(intptr_t n)
{
clock_t t = clock();
MD3 r_in = cspan_md(Vin, nx, ny, nz);
MD3 r_out = cspan_md(Vout, nx, ny, nz);
r_in = cspan_slice(MD3, &r_in, {lx, hx}, {ly, hy}, {lz, hz});
r_out = cspan_slice(MD3, &r_out, {lx, hx}, {ly, hy}, {lz, hz});
double sum = 0;
for (intptr_t s = 0; s < n; ++s) {
for (int x = 0; x < r_in.shape[0]; ++x) {
for (int y = 0; y < r_in.shape[1]; ++y) {
for (int z = 0; z < r_in.shape[2]; ++z)
{
double d = *cspan_at(&r_in, x,y,z);
*cspan_at(&r_out, x,y,z) += d;
sum += d;
}
}
}
}
t = clock() - t;
printf("nested : %.1f ms, %f\n", 1000.0f*t / CLOCKS_PER_SEC, sum);
}
int main(void)
{
intptr_t n = 100000;
for (int i = 0; i < nx * ny * nz; ++i)
Vin[i] = i + 1.23;
Traditional_for_loop(n);
MDRanges_loop_over_joined(n);
MDRanges_nested_loop(n);
}
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