Created
July 29, 2020 04:09
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Comparison of jsonArray printing methods. I have no idea why, but for some reason the generic approach is virtually the same speed as the specific approach. Almost as if the function call overhead is negligible.
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <time.h> | |
typedef int Foo; | |
// repetitive approach | |
int foosToJsonArray(FILE *file, Foo *foos, int n) { | |
if (fputc('[', file) == EOF) { | |
return -1; | |
} | |
for (int i = 0; i < n; ++i) { | |
if (i > 0) { | |
if (fputs(", ", file) == EOF) { | |
return -1; | |
} | |
} | |
if (fprintf(file, "foo: %d", foos[i]) < 0) { | |
return -1; | |
} | |
} | |
if (fputc(']', file) == EOF) { | |
return -1; | |
} | |
return 0; | |
} | |
// generic approach | |
int jsonArray(FILE *file, void *context, int(*hasNext)(void *context), int(*next)(FILE *file, void *context)) { | |
if (fputc('[', file) == EOF) { | |
return -1; | |
} | |
int first = 1; | |
while (hasNext(context)) { | |
if (first) { | |
first = 0; | |
} else { | |
if (fputs(", ", file) == EOF) { | |
return -1; | |
} | |
} | |
if (next(file, context)) { | |
return -1; | |
} | |
} | |
if (fputc(']', file) == EOF) { | |
return -1; | |
} | |
return 0; | |
} | |
typedef struct { | |
int i; | |
int n; | |
Foo *foos; | |
} FooPrinter; | |
int FooPrinter_hasNext(void *context) { | |
FooPrinter *printer = context; | |
return printer->i < printer->n; | |
} | |
int FooPrinter_next(FILE *file, void *context) { | |
FooPrinter *printer = context; | |
if (printer->i >= printer->n) { | |
fprintf(stderr, "index out of bounds: %d/%d\n", printer->i, printer->n); | |
exit(EXIT_FAILURE); | |
} | |
if (fprintf(file, "foo: %d", printer->foos[printer->i]) < 0) { | |
return -1; | |
} | |
++printer->i; | |
return 0; | |
} | |
void startProfile(struct timespec *start) { | |
clock_gettime(CLOCK_MONOTONIC, start); | |
} | |
void endProfile(struct timespec *start, double *timeMs) { | |
struct timespec end; | |
clock_gettime(CLOCK_MONOTONIC, &end); | |
*timeMs += (double) (end.tv_sec - start->tv_sec) * 1e3 + (double) (end.tv_nsec - start->tv_nsec) * 1e-6; | |
} | |
void printResults(const char *name, double totalTime, int numTrials) { | |
printf("\033[1;32m%10s\033[0m strategy took \033[1;30m%6.2fms\033[0m on average\n", name, totalTime / (double) numTrials); | |
} | |
int main(int argc, char **argv) { | |
int n = 1024 * 1024; | |
Foo *foos = malloc(sizeof(Foo) * n); | |
FooPrinter context = {0, n, foos}; | |
FILE *file = fopen("/dev/null", "w"); | |
struct timespec start; | |
double totalTimeSpecific = 0.0; | |
double totalTimeGeneric = 0.0; | |
int numTrials = 10; | |
for (int i = 0; i < numTrials; ++i) { | |
startProfile(&start); | |
foosToJsonArray(file, foos, n); | |
endProfile(&start, &totalTimeSpecific); | |
context = (FooPrinter) {0, n, foos}; | |
startProfile(&start); | |
jsonArray(file, &context, FooPrinter_hasNext, FooPrinter_next); | |
endProfile(&start, &totalTimeGeneric); | |
} | |
printResults("specific", totalTimeSpecific, numTrials); | |
printResults("generic", totalTimeGeneric, numTrials); | |
} |
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gcc -Ofast json.c && cmod +x a.out && ./a.out |
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