commit ff3685766b18c89ffb753de753e16ed38693c31b
parent ef04e0349a5f3a4701b9471508b63e1bb3558a75
Author: NunoSempere <nuno.sempere@protonmail.com>
Date: Fri, 2 Jun 2023 16:00:49 -0600
reorganize C code
Diffstat:
18 files changed, 623 insertions(+), 797 deletions(-)
diff --git a/C-optimized/README.md b/C-optimized/README.md
@@ -1,32 +0,0 @@
-# C-Optimized
-
-An optimized version of the original C implementation.
-
-The main changes are:
-
-- an optimization of the mixture function (it passes the functions instead of the whole arrays, reducing in great measure the memory usage and the computation time) and
-- the implementation of multi-threading with OpenMP.
-
-## Performance
-
-The mean time of execution is 6 ms. With the following distribution:
-
-
-
-The hardware used has been an AMD 5800x3D and 16GB of DDR4-3200 MHz.
-
-Also, the time data has been collected by executing the interior of the main() function 1000 times in a for loop, not executing the program itself 1000 times.
-
-## Multithreading
-
-Take into account that the multi-threading introduces a bit of dispersion in the execution time due to the creation and destruction of threads.
-
-In Nuño's machine, multithreading actually introduces a noticeable slowdown factor.
-
-## To do
-
-- [ ] Use proper profiling tool to capture timing with 1M samples.
-- [ ] Update above with correct timing
-- [ ] Add Windows/Powershell time-measuring commands
-- [ ] Add CUDA?
-- [ ] See if program can be reworded so as to use multithreading effectively, e.g., so that you see speed gains proportional to the number of threads used
diff --git a/C-optimized/makefile b/C-optimized/makefile
@@ -1,82 +0,0 @@
-# Interface:
-# make
-# make build
-# make format
-# make run
-
-# Compiler
-CC=gcc
-# CC=tcc # <= faster compilation
-
-# Main file
-SRC=samples.c
-OUTPUT=out/samples
-
-SRC_ONE_THREAD=./samples-one-thread.c
-OUTPUT_ONE_THREAD=out/samples-one-thread
-
-## Dependencies
-# Has no dependencies
-MATH=-lm
-
-## Flags
-DEBUG= #'-g'
-STANDARD=-std=c99
-WARNINGS=-Wall
-OPTIMIZED=-O3 #-O3 actually gives better performance than -Ofast, at least for this version
-OPENMP=-fopenmp
-
-## Formatter
-STYLE_BLUEPRINT=webkit
-FORMATTER=clang-format -i -style=$(STYLE_BLUEPRINT)
-
-## make build
-build: $(SRC)
- $(CC) $(OPTIMIZED) $(DEBUG) $(SRC) $(OPENMP) $(MATH) -o $(OUTPUT)
- $(CC) $(OPTIMIZED) $(DEBUG) $(SRC_ONE_THREAD) $(OPENMP) $(MATH) -o $(OUTPUT_ONE_THREAD)
-
-format: $(SRC)
- $(FORMATTER) $(SRC)
-
-run: $(SRC) $(OUTPUT)
- OMP_NUM_THREADS=1 ./$(OUTPUT) && echo
- ./$(OUTPUT_ONE_THREAD)
-
-multi:
- OMP_NUM_THREADS=1 ./$(OUTPUT) && echo
- OMP_NUM_THREADS=2 ./$(OUTPUT) && echo
- OMP_NUM_THREADS=4 ./$(OUTPUT) && echo
- OMP_NUM_THREADS=8 ./$(OUTPUT) && echo
- OMP_NUM_THREADS=16 ./$(OUTPUT) && echo
- ./$(OUTPUT_ONE_THREAD) && echo
-
-time-linux-simple:
- @echo "Requires /bin/time, found on GNU/Linux systems" && echo
- OMP_NUM_THREADS=1 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
- OMP_NUM_THREADS=2 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
- OMP_NUM_THREADS=4 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
- OMP_NUM_THREADS=8 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
- OMP_NUM_THREADS=16 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
- /bin/time -f "Time: %es" ./$(OUTPUT_ONE_THREAD) && echo
-
-time-linux:
- @echo "Requires /bin/time, found on GNU/Linux systems" && echo
-
- @echo "Running 100x and taking avg time: OMP_NUM_THREADS=1 $(OUTPUT)"
- @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=1 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 1 thread: |" | sed 's|$$|ms|' && echo
-
- @echo "Running 100x and taking avg time: OMP_NUM_THREADS=2 $(OUTPUT)"
- @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=2 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 2 threads: |" | sed 's|$$|ms|' && echo
-
- @echo "Running 100x and taking avg time: OMP_NUM_THREADS=4 $(OUTPUT)"
- @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=4 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time for 4 threads: |" | sed 's|$$|ms|' && echo
-
- @echo "Running 100x and taking avg time: OMP_NUM_THREADS=8 $(OUTPUT)"
- @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=8 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 8 threads: |" | sed 's|$$|ms|' && echo
-
- @echo "Running 100x and taking avg time: OMP_NUM_THREADS=16 $(OUTPUT)"
- @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=16 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 16 threads: |" | sed 's|$$|ms|' && echo
-
-debian-install-dependencies:
- sudo apt-get install libomp-dev
-
diff --git a/C-optimized/samples-one-thread.c b/C-optimized/samples-one-thread.c
@@ -1,183 +0,0 @@
-#include <math.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <time.h>
-
-const float PI = 3.14159265358979323846;
-
-#define N 10000000
-
-//Array helpers
-
-void array_print(float* array, int length)
-{
- for (int i = 0; i < length; i++) {
- printf("item[%d] = %f\n", i, array[i]);
- }
- printf("\n");
-}
-
-void array_fill(float* array, int length, float item)
-{
- int i;
- {
- for (i = 0; i < length; i++) {
- array[i] = item;
- }
- }
-}
-
-float array_sum(float* array, int length)
-{
- float output = 0.0;
- for (int i = 0; i < length; i++) {
- output += array[i];
- }
- return output;
-}
-
-void array_cumsum(float* array_to_sum, float* array_cumsummed, int length)
-{
- array_cumsummed[0] = array_to_sum[0];
- for (int i = 1; i < length; i++) {
- array_cumsummed[i] = array_cumsummed[i - 1] + array_to_sum[i];
- }
-}
-
-float rand_float(float to)
-{
- return ((float)rand() / (float)RAND_MAX) * to;
-}
-
-float ur_normal()
-{
- float u1 = rand_float(1.0);
- float u2 = rand_float(1.0);
- float z = sqrtf(-2.0 * log(u1)) * sin(2 * PI * u2);
- return z;
-}
-
-inline float random_uniform(float from, float to)
-{
- return ((float)rand() / (float)RAND_MAX) * (to - from) + from;
-}
-
-inline float random_normal(float mean, float sigma)
-{
- return (mean + sigma * ur_normal());
-}
-
-inline float random_lognormal(float logmean, float logsigma)
-{
- return expf(random_normal(logmean, logsigma));
-}
-
-inline float random_to(float low, float high)
-{
- const float NORMAL95CONFIDENCE = 1.6448536269514722;
- float loglow = logf(low);
- float loghigh = logf(high);
- float logmean = (loglow + loghigh) / 2;
- float logsigma = (loghigh - loglow) / (2.0 * NORMAL95CONFIDENCE);
- return random_lognormal(logmean, logsigma);
-}
-
-void array_random_to(float* array, int length, float low, float high)
-{
- int i;
- #pragma omp private(i)
- {
- #pragma omp for
- for (i = 0; i < length; i++) {
- array[i] = random_to(low, high);
- }
- }
-}
-
-void mixture(float (*samplers[])(void), float* weights, int n_dists, float* results, int results_length)
-{
- float sum_weights = array_sum(weights, n_dists);
- float* normalized_weights = malloc(n_dists * sizeof(float));
- for (int i = 0; i < n_dists; i++) {
- normalized_weights[i] = weights[i] / sum_weights;
- }
-
- float* cummulative_weights = malloc(n_dists * sizeof(float));
- array_cumsum(normalized_weights, cummulative_weights, n_dists);
-
- //create var holders
- float p1;
- int sample_index, i, own_length;
-
- {
- for (int i = 0; i < results_length; i++) {
- p1 = random_uniform(0, 1);
- for (int j = 0; j < n_dists; j++) {
- if (p1 < cummulative_weights[j]) {
- results[i] = samplers[j]();
- break;
- }
- }
- }
- }
- free(normalized_weights);
- free(cummulative_weights);
-}
-
-float sample_0()
-{
- return 0;
-}
-
-float sample_1()
-{
- return 1;
-}
-
-float sample_few()
-{
- return random_to(1, 3);
-}
-
-float sample_many()
-{
- return random_to(2, 10);
-}
-
-int main()
-{
- //initialize randomness
- srand(1);
-
- // clock_t start, end;
- // start = clock();
-
- // Toy example
- // Declare variables in play
- float p_a, p_b, p_c;
- // printf("Max threads: %d\n", n_threads);
- // omp_set_num_threads(n_threads);
-
- // Initialize variables
- p_a = 0.8;
- p_b = 0.5;
- p_c = p_a * p_b;
-
- // Generate mixture
- int n_dists = 4;
- float weights[] = { 1 - p_c, p_c / 2, p_c / 4, p_c / 4 };
- float (*samplers[])(void) = { sample_0, sample_1, sample_few, sample_many };
-
- float* results = malloc(N * sizeof(float));
- mixture(samplers, weights, n_dists, results, N);
- printf("Sum(dist_mixture, N)/N = %f\n", array_sum(results, N) / N);
- // array_print(dist_mixture[0], N);
-
- // end = clock();
- // printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC * 1000));
- // ^ Will only measure how long it takes the inner main to run, not the whole program,
- // including e.g., loading the program into memory or smth.
- // Also CLOCKS_PER_SEC in POSIX is a constant equal to 1000000.
- // See: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
- return 0;
-}
diff --git a/C-optimized/samples.c b/C-optimized/samples.c
@@ -1,281 +0,0 @@
-#include <math.h>
-#include <omp.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <time.h>
-
-const float PI = 3.14159265358979323846;
-
-#define N 1000000
-
-//Array helpers
-
-void array_print(float* array, int length)
-{
- for (int i = 0; i < length; i++) {
- printf("item[%d] = %f\n", i, array[i]);
- }
- printf("\n");
-}
-
-void array_fill(float* array, int length, float item)
-{
- int i;
- #pragma omp private(i)
- {
- #pragma omp for
- for (i = 0; i < length; i++) {
- array[i] = item;
- }
- }
-}
-
-float array_sum(float* array, int length)
-{
- float output = 0.0;
- for (int i = 0; i < length; i++) {
- output += array[i];
- }
- return output;
-}
-
-void array_cumsum(float* array_to_sum, float* array_cumsummed, int length)
-{
- array_cumsummed[0] = array_to_sum[0];
- for (int i = 1; i < length; i++) {
- array_cumsummed[i] = array_cumsummed[i - 1] + array_to_sum[i];
- }
-}
-
-float rand_float(float to, unsigned int* seed)
-{
- return ((float)rand_r(seed) / (float)RAND_MAX) * to;
- // See: <https://stackoverflow.com/questions/43151361/how-to-create-thread-safe-random-number-generator-in-c-using-rand-r>
- // rand() is not thread-safe, as it relies on (shared) hidden state.
-}
-
-float ur_normal(unsigned int* seed)
-{
- float u1 = rand_float(1.0, seed);
- float u2 = rand_float(1.0, seed);
- float z = sqrtf(-2.0 * log(u1)) * sin(2 * PI * u2);
- return z;
-}
-
-inline float random_uniform(float from, float to, unsigned int* seed)
-{
- return ((float) rand_r(seed) / (float)RAND_MAX) * (to - from) + from;
-}
-
-inline float random_normal(float mean, float sigma, unsigned int* seed)
-{
- return (mean + sigma * ur_normal(seed));
-}
-
-inline float random_lognormal(float logmean, float logsigma, unsigned int* seed)
-{
- return expf(random_normal(logmean, logsigma, seed));
-}
-
-inline float random_to(float low, float high, unsigned int* seed)
-{
- const float NORMAL95CONFIDENCE = 1.6448536269514722;
- float loglow = logf(low);
- float loghigh = logf(high);
- float logmean = (loglow + loghigh) / 2;
- float logsigma = (loghigh - loglow) / (2.0 * NORMAL95CONFIDENCE);
- return random_lognormal(logmean, logsigma, seed);
-}
-
-int split_array_get_my_length(int index, int total_length, int n_threads)
-{
- return (total_length % n_threads > index ? total_length / n_threads + 1 : total_length / n_threads);
-}
-
-//Old version, don't use it!! Optimized version is called mixture_f. This one is just for display
-/*
-void mixture(float* dists[], float* weights, int n_dists, float* results)
-{
- float sum_weights = array_sum(weights, n_dists);
- float* normalized_weights = malloc(n_dists * sizeof(float));
- for (int i = 0; i < n_dists; i++) {
- normalized_weights[i] = weights[i] / sum_weights;
- }
-
- float* cummulative_weights = malloc(n_dists * sizeof(float));
- array_cumsum(normalized_weights, cummulative_weights, n_dists);
-
- //create var holders
- float p1, p2;
- int index_found, index_counter, sample_index, i;
-
- #pragma omp parallel private(i, p1, p2, index_found, index_counter, sample_index)
- {
- #pragma omp for
- for (i = 0; i < N; i++) {
- p1 = random_uniform(0, 1);
- p2 = random_uniform(0, 1);
-
- index_found = 0;
- index_counter = 0;
-
- while ((index_found == 0) && (index_counter < n_dists)) {
- if (p1 < cummulative_weights[index_counter]) {
- index_found = 1;
- } else {
- index_counter++;
- }
- }
- if (index_found != 0) {
- sample_index = (int)(p2 * N);
- results[i] = dists[index_counter][sample_index];
- } else
- printf("This shouldn't be able to happen.\n");
- }
- }
- free(normalized_weights);
- free(cummulative_weights);
-}
-*/
-void mixture_f(float (*samplers[])(unsigned int* ), float* weights, int n_dists, float** results, int n_threads)
-{
- float sum_weights = array_sum(weights, n_dists);
- float* normalized_weights = malloc(n_dists * sizeof(float));
- for (int i = 0; i < n_dists; i++) {
- normalized_weights[i] = weights[i] / sum_weights;
- }
-
- float* cummulative_weights = malloc(n_dists * sizeof(float));
- array_cumsum(normalized_weights, cummulative_weights, n_dists);
-
- //create var holders
- float p1;
- int sample_index, i, own_length;
- unsigned int* seeds[n_threads];
- for(unsigned int i=0; i<n_threads; i++){
- seeds[i] = malloc(sizeof(unsigned int));
- *seeds[i] = i;
- }
-
- #pragma omp parallel private(i, p1, sample_index, own_length)
- {
- #pragma omp for
- for (i = 0; i < n_threads; i++) {
- own_length = split_array_get_my_length(i, N, n_threads);
- for (int j = 0; j < own_length; j++) {
- p1 = random_uniform(0, 1, seeds[i]);
- for (int k = 0; k < n_dists; k++) {
- if (p1 < cummulative_weights[k]) {
- results[i][j] = samplers[k](seeds[i]);
- break;
- }
- }
- }
- }
- }
- free(normalized_weights);
- free(cummulative_weights);
- for(unsigned int i=0; i<n_threads; i++){
- free(seeds[i]);
- }
-}
-
-float sample_0(unsigned int* seed)
-{
- return 0;
-}
-
-float sample_1(unsigned int* seed)
-{
- return 1;
-}
-
-float sample_few(unsigned int* seed)
-{
- return random_to(1, 3, seed);
-}
-
-float sample_many(unsigned int* seed)
-{
- return random_to(2, 10, seed);
-}
-
-void split_array_allocate(float** meta_array, int length, int divide_into)
-{
- int own_length;
-
- for (int i = 0; i < divide_into; i++) {
- own_length = split_array_get_my_length(i, length, divide_into);
- meta_array[i] = malloc(own_length * sizeof(float));
- }
-}
-
-void split_array_free(float** meta_array, int divided_into)
-{
- for (int i = 0; i < divided_into; i++) {
- free(meta_array[i]);
- }
- free(meta_array);
-}
-
-float split_array_sum(float** meta_array, int length, int divided_into)
-{
- int i;
- float output;
- float* partial_sum = malloc(divided_into * sizeof(float));
-
- #pragma omp private(i) shared(partial_sum)
- for (int i = 0; i < divided_into; i++) {
- float own_partial_sum = 0;
- int own_length = split_array_get_my_length(i, length, divided_into);
- for (int j = 0; j < own_length; j++) {
- own_partial_sum += meta_array[i][j];
- }
- partial_sum[i] = own_partial_sum;
- }
- for (int i = 0; i < divided_into; i++) {
- output += partial_sum[i];
- }
- return output;
-}
-
-int main()
-{
- //initialize randomness
- srand(time(NULL));
-
- // clock_t start, end;
- // start = clock();
-
- // Toy example
- // Declare variables in play
- float p_a, p_b, p_c;
- int n_threads = omp_get_max_threads();
- // printf("Max threads: %d\n", n_threads);
- // omp_set_num_threads(n_threads);
- float** dist_mixture = malloc(n_threads * sizeof(float*));
- split_array_allocate(dist_mixture, N, n_threads);
-
- // Initialize variables
- p_a = 0.8;
- p_b = 0.5;
- p_c = p_a * p_b;
-
- // Generate mixture
- int n_dists = 4;
- float weights[] = { 1 - p_c, p_c / 2, p_c / 4, p_c / 4 };
- float (*samplers[])(unsigned int* ) = { sample_0, sample_1, sample_few, sample_many };
-
- mixture_f(samplers, weights, n_dists, dist_mixture, n_threads);
- printf("Sum(dist_mixture, N)/N = %f\n", split_array_sum(dist_mixture, N, n_threads) / N);
- // array_print(dist_mixture[0], N);
- split_array_free(dist_mixture, n_threads);
-
- // end = clock();
- // printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC) * 1000);
- // ^ Will only measure how long it takes the inner main to run, not the whole program,
- // including e.g., loading the program into memory or smth.
- // Also CLOCKS_PER_SEC in POSIX is a constant equal to 1000000.
- // See: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
- return 0;
-}
diff --git a/C/makefile b/C/C-01-simple/makefile
diff --git a/C/samples b/C/C-01-simple/samples
Binary files differ.
diff --git a/C/samples.c b/C/C-01-simple/samples.c
diff --git a/C/C-02-better-algorithm-one-thread/makefile b/C/C-02-better-algorithm-one-thread/makefile
@@ -0,0 +1,53 @@
+# Interface:
+# make
+# make build
+# make format
+# make run
+
+# Compiler
+CC=gcc
+# CC=tcc # <= faster compilation
+
+# Main file
+
+SRC_ONE_THREAD=./samples-one-thread.c
+OUTPUT_ONE_THREAD=out/samples-one-thread
+
+## Dependencies
+# Has no dependencies
+MATH=-lm
+
+## Flags
+DEBUG= #'-g'
+STANDARD=-std=c99
+WARNINGS=-Wall
+OPTIMIZED=-O3 #-O3 actually gives better performance than -Ofast, at least for this version
+OPENMP=-fopenmp
+
+## Formatter
+STYLE_BLUEPRINT=webkit
+FORMATTER=clang-format -i -style=$(STYLE_BLUEPRINT)
+
+## make build
+build: $(SRC_ONE_THREAD)
+ mkdir -p out
+ $(CC) $(OPTIMIZED) $(DEBUG) $(SRC_ONE_THREAD) $(OPENMP) $(MATH) -o $(OUTPUT_ONE_THREAD)
+
+format: $(SRC_ONE_THREAD)
+ $(FORMATTER) $(SRC_ONE_THREAD)
+
+run: $(SRC_ONE_THREAD) $(OUTPUT_ONE_THREAD)
+ ./$(OUTPUT_ONE_THREAD)
+
+time-linux:
+ @echo "Requires /bin/time, found on GNU/Linux systems" && echo
+ @echo "Running 100x and taking avg time: $(OUTPUT_ONE_THREAD)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do $(OUTPUT_ONE_THREAD); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time: |" | sed 's|$$|ms|' && echo
+
+time-linux-simple:
+ @echo "Requires /bin/time, found on GNU/Linux systems" && echo
+ /bin/time -f "Time: %es" ./$(OUTPUT_ONE_THREAD) && echo
+
+debian-install-dependencies:
+ sudo apt-get install libomp-dev
+
diff --git a/C/C-02-better-algorithm-one-thread/out/samples-one-thread b/C/C-02-better-algorithm-one-thread/out/samples-one-thread
Binary files differ.
diff --git a/C/C-02-better-algorithm-one-thread/samples-one-thread.c b/C/C-02-better-algorithm-one-thread/samples-one-thread.c
@@ -0,0 +1,183 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+const float PI = 3.14159265358979323846;
+
+#define N 1000000
+
+//Array helpers
+
+void array_print(float* array, int length)
+{
+ for (int i = 0; i < length; i++) {
+ printf("item[%d] = %f\n", i, array[i]);
+ }
+ printf("\n");
+}
+
+void array_fill(float* array, int length, float item)
+{
+ int i;
+ {
+ for (i = 0; i < length; i++) {
+ array[i] = item;
+ }
+ }
+}
+
+float array_sum(float* array, int length)
+{
+ float output = 0.0;
+ for (int i = 0; i < length; i++) {
+ output += array[i];
+ }
+ return output;
+}
+
+void array_cumsum(float* array_to_sum, float* array_cumsummed, int length)
+{
+ array_cumsummed[0] = array_to_sum[0];
+ for (int i = 1; i < length; i++) {
+ array_cumsummed[i] = array_cumsummed[i - 1] + array_to_sum[i];
+ }
+}
+
+float rand_float(float to)
+{
+ return ((float)rand() / (float)RAND_MAX) * to;
+}
+
+float ur_normal()
+{
+ float u1 = rand_float(1.0);
+ float u2 = rand_float(1.0);
+ float z = sqrtf(-2.0 * log(u1)) * sin(2 * PI * u2);
+ return z;
+}
+
+inline float random_uniform(float from, float to)
+{
+ return ((float)rand() / (float)RAND_MAX) * (to - from) + from;
+}
+
+inline float random_normal(float mean, float sigma)
+{
+ return (mean + sigma * ur_normal());
+}
+
+inline float random_lognormal(float logmean, float logsigma)
+{
+ return expf(random_normal(logmean, logsigma));
+}
+
+inline float random_to(float low, float high)
+{
+ const float NORMAL95CONFIDENCE = 1.6448536269514722;
+ float loglow = logf(low);
+ float loghigh = logf(high);
+ float logmean = (loglow + loghigh) / 2;
+ float logsigma = (loghigh - loglow) / (2.0 * NORMAL95CONFIDENCE);
+ return random_lognormal(logmean, logsigma);
+}
+
+void array_random_to(float* array, int length, float low, float high)
+{
+ int i;
+ #pragma omp private(i)
+ {
+ #pragma omp for
+ for (i = 0; i < length; i++) {
+ array[i] = random_to(low, high);
+ }
+ }
+}
+
+void mixture(float (*samplers[])(void), float* weights, int n_dists, float* results, int results_length)
+{
+ float sum_weights = array_sum(weights, n_dists);
+ float* normalized_weights = malloc(n_dists * sizeof(float));
+ for (int i = 0; i < n_dists; i++) {
+ normalized_weights[i] = weights[i] / sum_weights;
+ }
+
+ float* cummulative_weights = malloc(n_dists * sizeof(float));
+ array_cumsum(normalized_weights, cummulative_weights, n_dists);
+
+ //create var holders
+ float p1;
+ int sample_index, i, own_length;
+
+ {
+ for (int i = 0; i < results_length; i++) {
+ p1 = random_uniform(0, 1);
+ for (int j = 0; j < n_dists; j++) {
+ if (p1 < cummulative_weights[j]) {
+ results[i] = samplers[j]();
+ break;
+ }
+ }
+ }
+ }
+ free(normalized_weights);
+ free(cummulative_weights);
+}
+
+float sample_0()
+{
+ return 0;
+}
+
+float sample_1()
+{
+ return 1;
+}
+
+float sample_few()
+{
+ return random_to(1, 3);
+}
+
+float sample_many()
+{
+ return random_to(2, 10);
+}
+
+int main()
+{
+ //initialize randomness
+ srand(1);
+
+ // clock_t start, end;
+ // start = clock();
+
+ // Toy example
+ // Declare variables in play
+ float p_a, p_b, p_c;
+ // printf("Max threads: %d\n", n_threads);
+ // omp_set_num_threads(n_threads);
+
+ // Initialize variables
+ p_a = 0.8;
+ p_b = 0.5;
+ p_c = p_a * p_b;
+
+ // Generate mixture
+ int n_dists = 4;
+ float weights[] = { 1 - p_c, p_c / 2, p_c / 4, p_c / 4 };
+ float (*samplers[])(void) = { sample_0, sample_1, sample_few, sample_many };
+
+ float* results = malloc(N * sizeof(float));
+ mixture(samplers, weights, n_dists, results, N);
+ printf("Sum(dist_mixture, N)/N = %f\n", array_sum(results, N) / N);
+ // array_print(dist_mixture[0], N);
+
+ // end = clock();
+ // printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC * 1000));
+ // ^ Will only measure how long it takes the inner main to run, not the whole program,
+ // including e.g., loading the program into memory or smth.
+ // Also CLOCKS_PER_SEC in POSIX is a constant equal to 1000000.
+ // See: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
+ return 0;
+}
diff --git a/C/README.md b/C/README.md
@@ -0,0 +1,15 @@
+# Time to BOTEC in C
+
+This repository contains a few implementations of a simple botec (back-of-the-envelope) calculation in C:
+
+- In the folder C-01-simple/, you can see a simple implementation, which passes large arrays
+- In the folder C-02-better-algorithm-one-thread/ you can see a better implementations, that passes around pointers to functions, which makes the implementation more efficient
+- In the top level, you can see an implementation that uses the better implementation in C-02..., and that also implements multithreading using OpenMP
+
+## To do
+
+- [ ] Update repository with correct timing
+- [ ] Add Windows/Powershell time-measuring commands
+- [ ] Add CUDA?
+- [x] Use better profiling approach to capture timing with 1M samples.
+- [x] See if program can be reworded so as to use multithreading effectively, e.g., so that you see speed gains proportional to the number of threads used
diff --git a/C/makefile b/C/makefile
@@ -1,53 +1,82 @@
-# Interface:
-# make
-# make build
-# make format
-# make run
-
-# Compiler
-CC=gcc
-# CC=tcc # <= faster compilation
-
-# Main file
-SRC=samples.c
-OUTPUT=samples
-
-## Dependencies
-DEPS='gsl'
-
-## Flags
-INCS=`pkg-config --cflags ${DEPS}`
-LIBS=`pkg-config --libs ${DEPS}`
-DEBUG= #'-g'
-STANDARD=-std=c99
-WARNINGS=-Wall
-FAST=-Ofast
-## Formatter
-STYLE_BLUEPRINT=webkit
-FORMATTER=clang-format -i -style=$(STYLE_BLUEPRINT)
-
-## make build
-build: $(SRC)
- $(CC) $(DEBUG) $(INCS) $(PLUGS) $(SRC) -o samples $(LIBS)
-
-fast: $(SRC)
- $(CC) $(FAST) $(DEBUG) $(INCS) $(PLUGS) $(SRC) -o samples $(LIBS)
-
-format: $(SRC)
- $(FORMATTER) $(SRC)
-
-run: $(SRC) $(OUTPUT)
- echo "Increasing stack size limit, because we are dealing with 1M samples"
- # ulimit: increase stack size limit
- # -Ss: the soft limit. If you set the hard limit, you then can't raise it
- # 256000: around 250Mbs, if I'm reading it correctly.
- # Then run the program
- ulimit -Ss 256000 && ./$(OUTPUT)
-
-
-
-# Old:
-# Link libraries, for good measure
-# LD_LIBRARY_PATH=/usr/local/lib
-# export LD_LIBRARY_PATH
-
+# Interface:
+# make
+# make build
+# make format
+# make run
+
+# Compiler
+CC=gcc
+# CC=tcc # <= faster compilation
+
+# Main file
+SRC=samples.c
+OUTPUT=out/samples
+
+SRC_ONE_THREAD=./samples-one-thread.c
+OUTPUT_ONE_THREAD=out/samples-one-thread
+
+## Dependencies
+# Has no dependencies
+MATH=-lm
+
+## Flags
+DEBUG= #'-g'
+STANDARD=-std=c99
+WARNINGS=-Wall
+OPTIMIZED=-O3 #-O3 actually gives better performance than -Ofast, at least for this version
+OPENMP=-fopenmp
+
+## Formatter
+STYLE_BLUEPRINT=webkit
+FORMATTER=clang-format -i -style=$(STYLE_BLUEPRINT)
+
+## make build
+build: $(SRC)
+ $(CC) $(OPTIMIZED) $(DEBUG) $(SRC) $(OPENMP) $(MATH) -o $(OUTPUT)
+ $(CC) $(OPTIMIZED) $(DEBUG) $(SRC_ONE_THREAD) $(OPENMP) $(MATH) -o $(OUTPUT_ONE_THREAD)
+
+format: $(SRC)
+ $(FORMATTER) $(SRC)
+
+run: $(SRC) $(OUTPUT)
+ OMP_NUM_THREADS=1 ./$(OUTPUT) && echo
+ ./$(OUTPUT_ONE_THREAD)
+
+multi:
+ OMP_NUM_THREADS=1 ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=2 ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=4 ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=8 ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=16 ./$(OUTPUT) && echo
+ ./$(OUTPUT_ONE_THREAD) && echo
+
+time-linux:
+ @echo "Requires /bin/time, found on GNU/Linux systems" && echo
+
+ @echo "Running 100x and taking avg time: OMP_NUM_THREADS=1 $(OUTPUT)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=1 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 1 thread: |" | sed 's|$$|ms|' && echo
+
+ @echo "Running 100x and taking avg time: OMP_NUM_THREADS=2 $(OUTPUT)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=2 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 2 threads: |" | sed 's|$$|ms|' && echo
+
+ @echo "Running 100x and taking avg time: OMP_NUM_THREADS=4 $(OUTPUT)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=4 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time for 4 threads: |" | sed 's|$$|ms|' && echo
+
+ @echo "Running 100x and taking avg time: OMP_NUM_THREADS=8 $(OUTPUT)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=8 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 8 threads: |" | sed 's|$$|ms|' && echo
+
+ @echo "Running 100x and taking avg time: OMP_NUM_THREADS=16 $(OUTPUT)"
+ @t=$$(/usr/bin/time -f "%e" -p bash -c 'for i in {1..100}; do OMP_NUM_THREADS=16 $(OUTPUT); done' 2>&1 >/dev/null | grep real | awk '{print $$2}' ); echo "scale=2; 1000 * $$t / 100" | bc | sed "s|^|Time using 16 threads: |" | sed 's|$$|ms|' && echo
+
+time-linux-simple:
+ @echo "Requires /bin/time, found on GNU/Linux systems" && echo
+ OMP_NUM_THREADS=1 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=2 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=4 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=8 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+ OMP_NUM_THREADS=16 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+ /bin/time -f "Time: %es" ./$(OUTPUT_ONE_THREAD) && echo
+
+debian-install-dependencies:
+ sudo apt-get install libomp-dev
+
diff --git a/C-optimized/out/samples b/C/out/samples
Binary files differ.
diff --git a/C-optimized/out/samples-one-thread b/C/out/samples-one-thread
Binary files differ.
diff --git a/C-optimized/out/samples.exe b/C/out/samples.exe
Binary files differ.
diff --git a/C-optimized/out/samples.txt b/C/out/samples.txt
diff --git a/C/samples.c b/C/samples.c
@@ -1,157 +1,281 @@
-#include <gsl/gsl_randist.h>
-#include <gsl/gsl_rng.h>
-#include <math.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <time.h>
-
-#define N 1000000
-/*
- * For very high values of N, you will want to increase the maximum stack trace, otherwise you will suffer a segmentation fault
- * In Ubuntu/bash you can do this with $ ulimit -Ss 256000 ## ~256Mbs
- * And confirm it with $ ulimit -a
-*/
-
-/* Helpers */
-void print(double* ys)
-{
- for (int i = 0; i < N; i++) {
- printf("%f\n", ys[i]);
- }
- printf("\n");
-}
-
-void fill(double* ys, float f)
-{
- for (int i = 0; i < N; i++) {
- ys[i] = f;
- }
-}
-
-double sum(double* ps, int n)
-{
- double result = 0;
- for (int i = 0; i < n; i++) {
- result += ps[i];
- }
- return (result);
-}
-
-void cumsum(double* ps, double* rs, int n)
-{
- double counter = 0;
- for (int i = 0; i < n; i++) {
- counter += ps[i];
- rs[i] = counter;
- }
-}
-
-/* Distributions*/
-void normal(gsl_rng* r, double* ys, double mean, double std)
-{
- for (int i = 0; i < N; i++) {
- ys[i] = mean + gsl_ran_gaussian(r, std);
- }
-}
-
-void lognormal(gsl_rng* r, double* ys, double zeta, double sigma)
-{
- for (int i = 0; i < N; i++) {
- ys[i] = gsl_ran_lognormal(r, zeta, sigma);
- }
-}
-
-void to(gsl_rng* r, double* ys, double low, double high)
-{
- double normal95confidencePoint = 1.6448536269514722;
- double log_low = log(low);
- double log_high = log(high);
- double zeta = (log_low + log_high) / 2;
- double sigma = (log_high - log_low) / (2.0 * normal95confidencePoint);
- lognormal(r, ys, zeta, sigma);
-}
-
-/* Mixture of distributions */
-void mixture(gsl_rng* r, double* dists[], double* weights, int n, double* results)
-{
- /* Get cummulative, normalized weights */
- double sum_weights = sum(weights, n);
- double normalized_weights[n];
- for (int i = 0; i < n; i++) {
- normalized_weights[i] = weights[i] / sum_weights;
- }
- double cummulative_weights[n];
- cumsum(normalized_weights, cummulative_weights, n);
-
- /* Get N samples, drawn from the different distributions in proportion to their weights. */
- for (int i = 0; i < N; i++) {
- double p_1 = gsl_rng_uniform(r);
- double p_2 = gsl_rng_uniform(r);
-
- int index_found = 0;
- int index_counter = 0;
- while ((index_found == 0) && (index_counter < n)) {
- if (p_1 < cummulative_weights[index_counter]) {
- index_found = 1;
- } else {
- index_counter++;
- }
- }
- if (index_found == 0) {
- printf("\nThis shouldn't be able to happen");
- // gsl_rng_free (r);
- // abort(); // this shouldn't have happened.
-
- } else {
- int sample_index = (int)floor(p_2 * N);
- results[i] = dists[index_counter][sample_index];
- }
- }
-}
-
-/* Main */
-int main(void)
-{
- // Start clock
- clock_t start, end;
- start = clock();
-
- /* Initialize GNU Statistical Library (GSL) stuff */
- const gsl_rng_type* T;
- gsl_rng* r;
- // gsl_rng_env_setup();
- T = gsl_rng_default;
- r = gsl_rng_alloc(T);
-
- /* Toy example */
- /* Declare variables in play */
- double p_a, p_b, p_c;
- double dist_none[N], dist_one[N], dist_few[N], dist_many[N], dist_mixture[N];
-
- /* Initialize variables */
- p_a = 0.8;
- p_b = 0.5;
- p_c = p_a * p_b;
-
- fill(dist_none, 0);
- fill(dist_one, 1);
- to(r, dist_few, 1, 3);
- to(r, dist_many, 2, 10);
-
- /* Generate mixture */
- int n = 4;
- double weights[] = { 1 - p_c, p_c / 2, p_c / 4, p_c / 4 };
- double* dists[] = { dist_none, dist_one, dist_few, dist_many };
-
- mixture(r, dists, weights, n, dist_mixture);
- printf("%f\n", sum(dist_mixture, N) / N);
-
- /* Clean up GSL */
- gsl_rng_free(r);
-
- // End clock
- end = clock();
- printf("Total time (ms): %f\n", ((double)(end - start)) / CLOCKS_PER_SEC * 1000);
- /* Return success*/
- return EXIT_SUCCESS;
-}
+#include <math.h>
+#include <omp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+const float PI = 3.14159265358979323846;
+
+#define N 1000000
+
+//Array helpers
+
+void array_print(float* array, int length)
+{
+ for (int i = 0; i < length; i++) {
+ printf("item[%d] = %f\n", i, array[i]);
+ }
+ printf("\n");
+}
+
+void array_fill(float* array, int length, float item)
+{
+ int i;
+ #pragma omp private(i)
+ {
+ #pragma omp for
+ for (i = 0; i < length; i++) {
+ array[i] = item;
+ }
+ }
+}
+
+float array_sum(float* array, int length)
+{
+ float output = 0.0;
+ for (int i = 0; i < length; i++) {
+ output += array[i];
+ }
+ return output;
+}
+
+void array_cumsum(float* array_to_sum, float* array_cumsummed, int length)
+{
+ array_cumsummed[0] = array_to_sum[0];
+ for (int i = 1; i < length; i++) {
+ array_cumsummed[i] = array_cumsummed[i - 1] + array_to_sum[i];
+ }
+}
+
+float rand_float(float to, unsigned int* seed)
+{
+ return ((float)rand_r(seed) / (float)RAND_MAX) * to;
+ // See: <https://stackoverflow.com/questions/43151361/how-to-create-thread-safe-random-number-generator-in-c-using-rand-r>
+ // rand() is not thread-safe, as it relies on (shared) hidden state.
+}
+
+float ur_normal(unsigned int* seed)
+{
+ float u1 = rand_float(1.0, seed);
+ float u2 = rand_float(1.0, seed);
+ float z = sqrtf(-2.0 * log(u1)) * sin(2 * PI * u2);
+ return z;
+}
+
+inline float random_uniform(float from, float to, unsigned int* seed)
+{
+ return ((float) rand_r(seed) / (float)RAND_MAX) * (to - from) + from;
+}
+
+inline float random_normal(float mean, float sigma, unsigned int* seed)
+{
+ return (mean + sigma * ur_normal(seed));
+}
+
+inline float random_lognormal(float logmean, float logsigma, unsigned int* seed)
+{
+ return expf(random_normal(logmean, logsigma, seed));
+}
+
+inline float random_to(float low, float high, unsigned int* seed)
+{
+ const float NORMAL95CONFIDENCE = 1.6448536269514722;
+ float loglow = logf(low);
+ float loghigh = logf(high);
+ float logmean = (loglow + loghigh) / 2;
+ float logsigma = (loghigh - loglow) / (2.0 * NORMAL95CONFIDENCE);
+ return random_lognormal(logmean, logsigma, seed);
+}
+
+int split_array_get_my_length(int index, int total_length, int n_threads)
+{
+ return (total_length % n_threads > index ? total_length / n_threads + 1 : total_length / n_threads);
+}
+
+//Old version, don't use it!! Optimized version is called mixture_f. This one is just for display
+/*
+void mixture(float* dists[], float* weights, int n_dists, float* results)
+{
+ float sum_weights = array_sum(weights, n_dists);
+ float* normalized_weights = malloc(n_dists * sizeof(float));
+ for (int i = 0; i < n_dists; i++) {
+ normalized_weights[i] = weights[i] / sum_weights;
+ }
+
+ float* cummulative_weights = malloc(n_dists * sizeof(float));
+ array_cumsum(normalized_weights, cummulative_weights, n_dists);
+
+ //create var holders
+ float p1, p2;
+ int index_found, index_counter, sample_index, i;
+
+ #pragma omp parallel private(i, p1, p2, index_found, index_counter, sample_index)
+ {
+ #pragma omp for
+ for (i = 0; i < N; i++) {
+ p1 = random_uniform(0, 1);
+ p2 = random_uniform(0, 1);
+
+ index_found = 0;
+ index_counter = 0;
+
+ while ((index_found == 0) && (index_counter < n_dists)) {
+ if (p1 < cummulative_weights[index_counter]) {
+ index_found = 1;
+ } else {
+ index_counter++;
+ }
+ }
+ if (index_found != 0) {
+ sample_index = (int)(p2 * N);
+ results[i] = dists[index_counter][sample_index];
+ } else
+ printf("This shouldn't be able to happen.\n");
+ }
+ }
+ free(normalized_weights);
+ free(cummulative_weights);
+}
+*/
+void mixture_f(float (*samplers[])(unsigned int* ), float* weights, int n_dists, float** results, int n_threads)
+{
+ float sum_weights = array_sum(weights, n_dists);
+ float* normalized_weights = malloc(n_dists * sizeof(float));
+ for (int i = 0; i < n_dists; i++) {
+ normalized_weights[i] = weights[i] / sum_weights;
+ }
+
+ float* cummulative_weights = malloc(n_dists * sizeof(float));
+ array_cumsum(normalized_weights, cummulative_weights, n_dists);
+
+ //create var holders
+ float p1;
+ int sample_index, i, own_length;
+ unsigned int* seeds[n_threads];
+ for(unsigned int i=0; i<n_threads; i++){
+ seeds[i] = malloc(sizeof(unsigned int));
+ *seeds[i] = i;
+ }
+
+ #pragma omp parallel private(i, p1, sample_index, own_length)
+ {
+ #pragma omp for
+ for (i = 0; i < n_threads; i++) {
+ own_length = split_array_get_my_length(i, N, n_threads);
+ for (int j = 0; j < own_length; j++) {
+ p1 = random_uniform(0, 1, seeds[i]);
+ for (int k = 0; k < n_dists; k++) {
+ if (p1 < cummulative_weights[k]) {
+ results[i][j] = samplers[k](seeds[i]);
+ break;
+ }
+ }
+ }
+ }
+ }
+ free(normalized_weights);
+ free(cummulative_weights);
+ for(unsigned int i=0; i<n_threads; i++){
+ free(seeds[i]);
+ }
+}
+
+float sample_0(unsigned int* seed)
+{
+ return 0;
+}
+
+float sample_1(unsigned int* seed)
+{
+ return 1;
+}
+
+float sample_few(unsigned int* seed)
+{
+ return random_to(1, 3, seed);
+}
+
+float sample_many(unsigned int* seed)
+{
+ return random_to(2, 10, seed);
+}
+
+void split_array_allocate(float** meta_array, int length, int divide_into)
+{
+ int own_length;
+
+ for (int i = 0; i < divide_into; i++) {
+ own_length = split_array_get_my_length(i, length, divide_into);
+ meta_array[i] = malloc(own_length * sizeof(float));
+ }
+}
+
+void split_array_free(float** meta_array, int divided_into)
+{
+ for (int i = 0; i < divided_into; i++) {
+ free(meta_array[i]);
+ }
+ free(meta_array);
+}
+
+float split_array_sum(float** meta_array, int length, int divided_into)
+{
+ int i;
+ float output;
+ float* partial_sum = malloc(divided_into * sizeof(float));
+
+ #pragma omp private(i) shared(partial_sum)
+ for (int i = 0; i < divided_into; i++) {
+ float own_partial_sum = 0;
+ int own_length = split_array_get_my_length(i, length, divided_into);
+ for (int j = 0; j < own_length; j++) {
+ own_partial_sum += meta_array[i][j];
+ }
+ partial_sum[i] = own_partial_sum;
+ }
+ for (int i = 0; i < divided_into; i++) {
+ output += partial_sum[i];
+ }
+ return output;
+}
+
+int main()
+{
+ //initialize randomness
+ srand(time(NULL));
+
+ // clock_t start, end;
+ // start = clock();
+
+ // Toy example
+ // Declare variables in play
+ float p_a, p_b, p_c;
+ int n_threads = omp_get_max_threads();
+ // printf("Max threads: %d\n", n_threads);
+ // omp_set_num_threads(n_threads);
+ float** dist_mixture = malloc(n_threads * sizeof(float*));
+ split_array_allocate(dist_mixture, N, n_threads);
+
+ // Initialize variables
+ p_a = 0.8;
+ p_b = 0.5;
+ p_c = p_a * p_b;
+
+ // Generate mixture
+ int n_dists = 4;
+ float weights[] = { 1 - p_c, p_c / 2, p_c / 4, p_c / 4 };
+ float (*samplers[])(unsigned int* ) = { sample_0, sample_1, sample_few, sample_many };
+
+ mixture_f(samplers, weights, n_dists, dist_mixture, n_threads);
+ printf("Sum(dist_mixture, N)/N = %f\n", split_array_sum(dist_mixture, N, n_threads) / N);
+ // array_print(dist_mixture[0], N);
+ split_array_free(dist_mixture, n_threads);
+
+ // end = clock();
+ // printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC) * 1000);
+ // ^ Will only measure how long it takes the inner main to run, not the whole program,
+ // including e.g., loading the program into memory or smth.
+ // Also CLOCKS_PER_SEC in POSIX is a constant equal to 1000000.
+ // See: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
+ return 0;
+}
diff --git a/README.md b/README.md
@@ -29,15 +29,15 @@ As of now, it may be useful for checking the validity of simple estimations. The
## Comparison table
-| Language | Time | Lines of code |
-|--------------------------|-----------|---------------|
-| C (optimized, 1 thread) | 30ms | 183 |
-| Nim | 68ms | 84 |
-| C | 292ms | 149 |
-| Javascript (NodeJS) | 732ms | 69 |
-| Squiggle | 1,536s | 14 |
-| R | 7,000s | 49 |
-| Python (CPython) | 16,641s | 56 |
+| Language | Time | Lines of code |
+|-----------------------------|-----------|---------------|
+| C (optimized, 16 threads) | 6ms | 183 |
+| Nim | 68ms | 84 |
+| C (naïve implementation) | 292ms | 149 |
+| Javascript (NodeJS) | 732ms | 69 |
+| Squiggle | 1,536s | 14 |
+| R | 7,000s | 49 |
+| Python (CPython) | 16,641s | 56 |
Time measurements taken with the [time](https://man7.org/linux/man-pages/man1/time.1.html) tool, using 1M samples:
