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find_roots.c
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find_roots.c
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/*
Copyright (c) 2021 Blosc Development Team <[email protected]>
https://blosc.org
License: BSD 3-Clause (see LICENSE.txt)
Example program demonstrating how the different compression params affects
the performance of root finding.
To compile this program:
$ gcc -O3 find_roots.c -o find_roots -lblosc2
To run:
$ ./find_roots
Blosc version info: 2.0.0a6.dev ($Date:: 2018-05-18 #$)
Creation time for X values: 0.178 s, 4274.5 MB/s
Compression for X values: 762.9 MB -> 27.3 MB (28.0x)
Computing Y polynomial: 0.342 s, 4463.3 MB/s
Compression for Y values: 762.9 MB -> 54.0 MB (14.1x)
Roots found at: 1.350000023841858, 4.450000286102295, 8.500000953674316,
Find root time: 0.401 s, 3806.8 MB/s
*/
#include <stdio.h>
#include "blosc2.h"
#define KB 1024.
#define MB (1024*KB)
#define GB (1024*MB)
#define NCHUNKS 500
#define CHUNKSIZE (200 * 1000) // fits well in modern L3 caches
#define NTHREADS 4
void fill_buffer(double *x, int nchunk) {
double incx = 10. / (NCHUNKS * CHUNKSIZE);
for (int i = 0; i < CHUNKSIZE; i++) {
x[i] = incx * (nchunk * CHUNKSIZE + i);
}
}
void process_data(const double *x, double *y) {
for (int i = 0; i < CHUNKSIZE; i++) {
double xi = x[i];
//y[i] = ((.25 * xi + .75) * xi - 1.5) * xi - 2;
y[i] = (xi - 1.35) * (xi - 4.45) * (xi - 8.5);
}
}
void find_root(const double *x, const double *y,
const double prev_value) {
double pv = prev_value;
int last_root_idx = -1;
for (int i = 0; i < CHUNKSIZE; i++) {
double yi = y[i];
if (((yi > 0) - (yi < 0)) != ((pv > 0) - (pv < 0))) {
if (last_root_idx != (i - 1)) {
printf("%.16g, ", x[i]);
last_root_idx = i; // avoid the last point (ULP effects)
}
}
pv = yi;
}
}
int compute_vectors(void) {
static double buffer_x[CHUNKSIZE];
static double buffer_y[CHUNKSIZE];
const int32_t isize = CHUNKSIZE * sizeof(double);
int dsize;
long nbytes = 0;
blosc2_schunk *sc_x, *sc_y;
int nchunk;
blosc_timestamp_t last, current;
double ttotal;
double prev_value;
/* Create a super-chunk container for input (X values) */
blosc2_cparams cparams = BLOSC2_CPARAMS_DEFAULTS;
cparams.typesize = sizeof(double);
cparams.compcode = BLOSC_LZ4;
cparams.clevel = 9;
cparams.filters[0] = BLOSC_TRUNC_PREC;
cparams.filters_meta[0] = 23; // treat doubles as floats
cparams.nthreads = NTHREADS;
blosc2_dparams dparams = BLOSC2_DPARAMS_DEFAULTS;
dparams.nthreads = NTHREADS;
blosc2_storage storage = {.cparams=&cparams, .dparams=&dparams};
sc_x = blosc2_schunk_new(&storage);
/* Create a super-chunk container for output (Y values) */
sc_y = blosc2_schunk_new(&storage);
/* Now fill the buffer with even values between 0 and 10 */
blosc_set_timestamp(&last);
for (nchunk = 0; nchunk < NCHUNKS; nchunk++) {
fill_buffer(buffer_x, nchunk);
blosc2_schunk_append_buffer(sc_x, buffer_x, isize);
nbytes += (long) isize;
}
blosc_set_timestamp(¤t);
ttotal = blosc_elapsed_secs(last, current);
printf("Creation time for X values: %.3g s, %.1f MB/s\n",
ttotal, (double) nbytes / (ttotal * MB));
printf("Compression for X values: %.1f MB -> %.1f MB (%.1fx)\n",
(double)sc_x->nbytes / MB, (double)sc_x->cbytes / MB,
(1. * (double)sc_x->nbytes) / (double)sc_x->cbytes);
/* Retrieve the chunks and compute the polynomial in another super-chunk */
blosc_set_timestamp(&last);
for (nchunk = 0; nchunk < NCHUNKS; nchunk++) {
dsize = blosc2_schunk_decompress_chunk(sc_x, nchunk, buffer_x, isize);
if (dsize < 0) {
printf("Decompression error. Error code: %d\n", dsize);
return dsize;
}
process_data(buffer_x, buffer_y);
blosc2_schunk_append_buffer(sc_y, buffer_y, isize);
}
blosc_set_timestamp(¤t);
ttotal = blosc_elapsed_secs(last, current);
printf("Computing Y polynomial: %.3g s, %.1f MB/s\n",
ttotal, 2. * (double) nbytes / (ttotal * MB)); // 2 super-chunks involved
printf("Compression for Y values: %.1f MB -> %.1f MB (%.1fx)\n",
(double)sc_y->nbytes / MB, (double)sc_y->cbytes / MB,
(1. * (double)sc_y->nbytes) / (double)sc_y->cbytes);
/* Find the roots of the polynomial */
printf("Roots found at: ");
blosc_set_timestamp(&last);
prev_value = buffer_y[0];
for (nchunk = 0; nchunk < NCHUNKS; nchunk++) {
dsize = blosc2_schunk_decompress_chunk(sc_y, nchunk, (void *) buffer_y, isize);
if (dsize < 0) {
printf("Decompression error. Error code: %d\n", dsize);
return dsize;
}
dsize = blosc2_schunk_decompress_chunk(sc_x, nchunk, (void *) buffer_x, isize);
if (dsize < 0) {
printf("Decompression error. Error code: %d\n", dsize);
return dsize;
}
find_root(buffer_x, buffer_y, prev_value);
prev_value = buffer_y[CHUNKSIZE - 1];
}
blosc_set_timestamp(¤t);
ttotal = blosc_elapsed_secs(last, current);
printf("\n");
printf("Find root time: %.3g s, %.1f MB/s\n",
ttotal, 2. * (double) nbytes / (ttotal * MB)); // 2 super-chunks involved
/* Free resources */
/* Destroy the super-chunk */
blosc2_schunk_free(sc_x);
blosc2_schunk_free(sc_y);
return 0;
}
int main(void) {
printf("Blosc version info: %s (%s)\n",
BLOSC2_VERSION_STRING, BLOSC2_VERSION_DATE);
/* Initialize the Blosc compressor */
blosc2_init();
compute_vectors();
/* Destroy the Blosc environment */
blosc2_destroy();
return 0;
}