Safer push_back and faster push_back (I went from 0(n^2) to 0(1))

2026-04-17 10:48:42 -04:00
parent 03d30f3d0b
commit 81cd5c00e1
12 changed files with 1165 additions and 50 deletions
@@ -0,0 +1,95 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+typedef struct {
+    char* arr;
+    size_t size;
+} Vec8_t;
+
+Vec8_t create(size_t init_size) {
+    Vec8_t vec = { .arr = nullptr, .size = 0 };
+    if (init_size > 0) {
+        vec.arr = malloc(init_size * sizeof(char));
+        vec.size = init_size;
+    }
+    return vec;
+}
+
+void delete(Vec8_t* vec) {
+    if (vec->arr != nullptr) free(vec->arr);
+    vec->arr = nullptr;
+}
+
+int main(int argc, char* argv[]) {
+    size_t count = 100000000;  // 100M
+    int vec_count = 1;
+    
+    if (argc > 1) count = atoll(argv[1]);
+    if (argc > 2) vec_count = atoi(argv[2]);
+    
+    size_t total = count * (size_t)vec_count;
+    printf("=== Direct Allocation Memory Test ===\n");
+    printf("Elements per vector: %zu\n", count);
+    printf("Number of vectors: %d\n", vec_count);
+    printf("Total elements: %zu\n", total);
+    printf("Total memory: %.1f GB\n", (total * sizeof(char)) / (1024.0 * 1024.0 * 1024.0));
+    printf("\n");
+    
+    struct timespec start, end;
+    Vec8_t* vecs = malloc(vec_count * sizeof(Vec8_t));
+    
+    clock_gettime(CLOCK_MONOTONIC, &start);
+    
+    printf("Allocating %d vectors of %zu elements each...\n", vec_count, count);
+    for (int v = 0; v < vec_count; v++) {
+        vecs[v] = create(count);
+        if (vecs[v].arr == nullptr) {
+            printf("  ERROR: Failed to allocate vector %d!\n", v);
+            return 1;
+        }
+    }
+    
+    clock_gettime(CLOCK_MONOTONIC, &end);
+    double alloc_time = (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 1e9;
+    printf("Allocation time: %.2f seconds\n", alloc_time);
+    
+    printf("\nFilling vectors...\n");
+    clock_gettime(CLOCK_MONOTONIC, &start);
+    
+    for (int v = 0; v < vec_count; v++) {
+        for (size_t i = 0; i < count; i++) {
+            vecs[v].arr[i] = (char)(i % 256);
+        }
+    }
+    
+    clock_gettime(CLOCK_MONOTONIC, &end);
+    double fill_time = (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 1e9;
+    printf("Fill time: %.2f seconds\n", fill_time);
+    
+    printf("\nVerifying...\n");
+    int errors = 0;
+    for (int v = 0; v < vec_count; v++) {
+        if (vecs[v].size != count) errors++;
+        if (vecs[v].arr[0] != 0) errors++;
+        if (vecs[v].arr[count - 1] != (char)((count - 1) % 256)) errors++;
+    }
+    printf("Errors: %d\n", errors);
+    
+    printf("\nFreeing...\n");
+    clock_gettime(CLOCK_MONOTONIC, &start);
+    for (int v = 0; v < vec_count; v++) {
+        delete(&vecs[v]);
+    }
+    clock_gettime(CLOCK_MONOTONIC, &end);
+    double free_time = (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 1e9;
+    printf("Free time: %.2f seconds\n", free_time);
+    
+    free(vecs);
+    
+    printf("\n=== Complete ===\n");
+    printf("Total time: %.2f seconds\n", alloc_time + fill_time + free_time);
+    
+    return errors > 0 ? 1 : 0;
+}