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mauldin.c
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mauldin.c
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#include <assert.h>
#include <math.h>
#include <time.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
// app constants
#define NUM_THREADS 2
#define N 200000000LL / NUM_THREADS // fast
//#define N 10000000000LL / NUM_THREADS // produces nicely detailed image
#define NX 4000 // image width (pixels)
#define NY 4000 // image height (pixels)
#define SCALE (NX / 2)
// math constants
#define SQRT3 1.73205081f
#define SQRT1p5 1.22474487f
// each thread receives one of these
typedef struct thread_context {
unsigned int id;
float *image;
// used for locking image table when updating (default: not used)
pthread_mutex_t *image_mutex;
} thread_context;
inline void plot(float *image, float x, float y, float luma) {
int ix, iy, offset;
ix = (int)(x*SCALE + NX*0.5f);
iy = (int)(y*SCALE + NY*0.5f);
if (luma < 0)
luma = 0.0f;
if (ix >=0 && iy >= 0 && ix < NX && iy < NY) {
offset = NX*iy + ix;
// accumulating lumas produces nicely shaded image
image[offset] += luma;
}
}
void *mauldin(void *context) {
float x[3], y[3], xa, ya, xb, yb, xc, yc, fact, x_exact, y_exact;
float btl, btr, bbl, bbr, fx, fy;
int choice;
thread_context *t_context = (thread_context *)context;
float *image = t_context->image;
unsigned long long i;
// use unique thread id as srand seed
srand(t_context->id);
// random initial conditions
x[0] = (float)rand()/(float)RAND_MAX;
y[0] = (float)rand()/(float)RAND_MAX;
// don't render first 100 iterations
for (i = 0; i < 100; i++) {
choice = rand_r(&(t_context->id))%3;
x[1] = (-0.5f)*x[0] - 0.866025404f*y[0]; // xr == 1
y[1] = (-0.5f)*y[0] + 0.866025404f*x[0];
x[2] = x[1]*x[1] - y[1]*y[1]; // x2 == 2
y[2] = 2.0f * x[1] * y[1];
xa = (SQRT3-1.0f)*x[choice]+1.0f;
ya = (SQRT3-1.0f)*y[choice];
xb = -x[choice]+(SQRT3+1.0f);
yb = -y[choice];
fact = 1.0f / (xb*xb+yb*yb);
xc = xb * fact;
yc = -yb * fact;
x[0] = (xa*xc - ya*yc) * SQRT1p5;
y[0] = (xa*yc + xc*ya) * SQRT1p5;
}
for (i = 100; i < N; i++) {
choice = rand_r(&(t_context->id))%3;
x[1] = (-0.5f)*x[0] - 0.866025404f*y[0]; // xr == 1
y[1] = (-0.5f)*y[0] + 0.866025404f*x[0];
x[2] = x[1]*x[1] - y[1]*y[1]; // x2 == 2
y[2] = 2.0f * x[1] * y[1];
xa = (SQRT3-1.0f)*x[choice]+1;
ya = (SQRT3-1.0f)*y[choice];
xb = -x[choice]+(SQRT3+1.0f);
yb = -y[choice];
fact = 1.0f / (xb*xb+yb*yb);
xc = xb * fact;
yc = -yb * fact;
x[0] = (xa*xc - ya*yc) * SQRT1p5;
y[0] = (xa*yc + xc*ya) * SQRT1p5;
// bilinear interp
fx = x[0] - (int)x[0];
fy = y[0] - (int)y[0];
btl = (1.0f - fx) * (1.0f - fy);
btr = fx * (1.0f - fy);
bbl = (1.0f - fx) * fy;
bbr = fx * fy;
// Uncomment lock/unlock if you would like to be "correct" and avoid
// interference. Probability of interference is quite low, however,
// and using mutexes slows things down considerably.
//pthread_mutex_lock(t_context->image_mutex);
plot(image, x[0], y[0], btl);
plot(image, x[0]+1, y[0], btr);
plot(image, x[0], y[0]+1, bbl);
plot(image, x[0]+1, y[0]+1, bbr);
//pthread_mutex_unlock(t_context->image_mutex);
}
pthread_exit(NULL);
}
int main(int argc, char *argv[]) {
pthread_t threads[NUM_THREADS];
pthread_mutex_t image_mutex;
thread_context thread_contexts[NUM_THREADS];
FILE *outfile=NULL;
int rc, x, y, offset, k;
long t;
float max = 0, logmax = 0;
unsigned int luma, num_image_elems = NX*NY;
float *image = (float *)malloc(num_image_elems*sizeof(float));
// initialize mutex
pthread_mutex_init(&image_mutex, NULL);
clock_t start = clock();
for (t=0; t < NUM_THREADS; t++) {
thread_contexts[t].id = t;
thread_contexts[t].image = image;
thread_contexts[t].image_mutex = &image_mutex;
fprintf(stderr, "\nSpawning thread %ld", t);
rc = pthread_create(&threads[t], NULL, mauldin, (void *)&thread_contexts[t]);
if (rc) {
fprintf(stderr, "\nERROR; return code from pthread_create() is %d", rc);
exit(-1);
}
}
fprintf(stderr, "\nProcessing...");
for (t=0; t < NUM_THREADS; t++) {
rc = pthread_join(threads[t], NULL);
assert(rc == 0);
fprintf(stderr, "\nThread %ld finished.", t);
}
clock_t end = clock();
float cpu_time = ((float)(end - start))/((float)(CLOCKS_PER_SEC));
fprintf(stderr, "\nCLOCKS_PER_SEC: %ld", CLOCKS_PER_SEC);
fprintf(stderr, "\nclocks elapsed: %ld", (end - start));
fprintf(stderr, "\ncpu_time: %lf", cpu_time);
fprintf(stderr, "\niterations_per_sec: %e",(((float)N*NUM_THREADS)/cpu_time));
fprintf(stderr, "\n\nFinding maximum luminosity..");
for (k = 0; k < num_image_elems; k ++) {
if (image[k] > max)
max = image[k];
}
logmax = log(max + 1);
fprintf(stderr, "\nmax = %f, log(max + 1) = %f", max, logmax);
fprintf(stderr, "\nWriting image to file...");
// write image to PPM file
outfile = fopen("output.ppm", "w");
fprintf(outfile, "P2\n");
fprintf(outfile, "%d %d\n", NX, NY);
fprintf(outfile, "65535");
for (y = 0; y < NY; y++) {
fprintf(outfile, "\n");
for (x = 0; x < NX; x++) {
offset = NX*y+x;
luma = (unsigned int)(65535.0 * log(image[offset] + 1.0) / logmax);
assert(luma >= 0 && luma <= 65535);
fprintf(outfile, "%d ", luma);
}
}
fprintf(stderr, "Done.\n");
free(image);
close(outfile);
pthread_mutex_destroy(&image_mutex);
pthread_exit(NULL);
}