commit 49840162015a0faaa7e82e96f0fcbd272ea13010
Author: Intel A80486DX2-66 <larry.holst@disroot.org>
Date:   Wed Dec 27 17:35:59 2023 +0300

    add reverse-ramdisk.c

diff --git a/c-programming/reverse-ramdisk.c b/c-programming/reverse-ramdisk.c
new file mode 100644
index 0000000..9563393
--- /dev/null
+++ b/c-programming/reverse-ramdisk.c
@@ -0,0 +1,218 @@
+/*
+C programming idea: Handling temporary files like memory allocations (allocating -> creating empty file, using -> locking for R/W, freeing -> deleting).
+
+50% AI, 50% human (the code is tested and reviewed)
+
+GCC/Clang/TCC: Compile with -DTEST to set macro TEST as defined
+*/
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+	int ID;
+	char* file_path;
+	FILE* file;
+} TempFile;
+
+TempFile* temp_files = NULL;
+size_t num_temp_files = 0;
+
+#define line_fail(x) do { \
+	printf("failed on line %d\n", __LINE__ + x); \
+} while (0)
+
+int tf_alloc(size_t n, size_t type_size) {
+	// Create an empty file
+	char file_path[20];
+	sprintf(file_path, "tf_%zu.tmp", num_temp_files);
+	FILE* file = fopen(file_path, "w+b");
+	if (file == NULL) {
+		line_fail(-2);
+		return -1;
+	}
+
+	// Allocate memory for the TempFile struct
+	TempFile* temp_file = (TempFile*)malloc(sizeof(TempFile));
+	if (temp_file == NULL) {
+		line_fail(-2);
+		return -1;
+	}
+
+	// Assign the ID and file path
+	temp_file->ID = num_temp_files;
+	temp_file->file_path = strdup(file_path);
+	temp_file->file = file;
+
+	// Increase the number of temp files
+	num_temp_files++;
+
+	// Reallocate memory for the temp_files array
+	temp_files = (TempFile*)realloc(temp_files, num_temp_files * sizeof(TempFile));
+	if (temp_files == NULL) {
+		line_fail(-2);
+		return -1;
+	}
+
+	// Add the temp file to the array
+	temp_files[num_temp_files - 1] = *temp_file;
+
+	return temp_file->ID;
+}
+
+int tf_free(int ID) {
+	// Find the temp file with the given ID
+	int index = -1;
+	for (int i = 0; i < num_temp_files; i++)
+		if (temp_files[i].ID == ID) {
+			index = i;
+			break;
+		}
+
+	if (index == -1)
+		return -1;
+
+	fclose(temp_files[index].file);
+
+	// Delete the file
+	if (remove(temp_files[index].file_path) != 0) {
+		return -1;
+	}
+
+	free(temp_files[index].file_path);
+
+	// Shift the remaining temp files in the array
+	for (int i = index; i < num_temp_files - 1; i++) {
+		temp_files[i] = temp_files[i + 1];
+	}
+
+	// Decrease the number of temp files
+	num_temp_files--;
+
+	// Reallocate memory for the temp_files array
+	temp_files = (TempFile*)realloc(temp_files, num_temp_files * sizeof(TempFile));
+	if (temp_files == NULL && num_temp_files > 0) {
+		return -1;
+	}
+
+	return 0;
+}
+
+int tf_write(int ID, size_t offset, void* data, size_t data_size) {
+	// Find the temp file with the given ID
+	int index = -1;
+	for (int i = 0; i < num_temp_files; i++) {
+		if (temp_files[i].ID == ID) {
+			index = i;
+			break;
+		}
+	}
+
+	if (index == -1)
+		return -1;
+
+	// Open the file in append mode
+	FILE* file = temp_files[index].file;
+	if (file == NULL)
+		return -1;
+
+	// Seek
+	fseek(file, offset, SEEK_SET);
+
+	// Write the data to the file
+	size_t bytes_written = fwrite(data, 1, data_size, file);
+
+	if (bytes_written != data_size)
+		return -1;
+
+	return 0;
+}
+
+int tf_read(int ID, size_t offset, void* dest, size_t data_size) {
+	// Find the temp file with the given ID
+	int index = -1;
+	for (int i = 0; i < num_temp_files; i++) {
+		if (temp_files[i].ID == ID) {
+			index = i;
+			break;
+		}
+	}
+
+	if (index == -1) {
+		return -1;
+	}
+
+	// Open the file in read mode
+	FILE* file = temp_files[index].file;
+	if (file == NULL)
+		return -1;
+
+	// Read the data from the file
+	void* data = malloc(data_size);
+	if (data == NULL) {
+		fclose(file);
+		return -1;
+	}
+
+	// Initialize the memory in the data buffer
+	memset(data, 0, data_size);
+
+	fseek(file, offset, SEEK_SET);
+	size_t bytes_read = fread(data, 1, data_size, file);
+
+	// Copy the data to the destination pointer
+	memcpy(dest, data, data_size);
+
+	free(data); // Free the allocated memory
+
+	if (bytes_read != data_size) {
+		errno = EIO;
+		return -1;
+	}
+
+	printf("Read: ID = %d, data = %016" PRIXPTR ", size = %zu -> '",
+		ID, (uintptr_t)dest, data_size);
+	for (size_t i = 0; i < data_size; i++)
+		printf("0x%02" PRIX8 " ", *((uint8_t*)(dest + i)));
+	printf("'\n");
+	return 0;
+}
+
+#define retreat(s) do { \
+	perror(s); \
+	exit(EXIT_FAILURE); \
+} while (0)
+
+#ifdef TEST
+int main() {
+	int ID = tf_alloc(4, sizeof(int));
+	if (ID == -1)
+		retreat("tf_alloc");
+
+	int test_data[4] = {123, 456, 789, -123};
+
+	for (size_t i = 0; i < 4; i++)
+		if (tf_write(ID, i * sizeof(int), &test_data[i], sizeof(int)) == -1)
+			retreat("tf_write");
+
+	// round-trip
+	test_data[0] = 111;
+	test_data[1] = 222;
+	test_data[2] = 333;
+	test_data[3] = 444;
+
+	for (size_t i = 0; i < 4; i++)
+		if (tf_read(ID, i * sizeof(int), &test_data[i], sizeof(int)) == -1)
+			retreat("tf_read");
+
+	printf("Values: %d %d %d %d\n",
+		test_data[0], test_data[1], test_data[2], test_data[3]);
+
+	tf_free(ID);
+
+	return 0;
+}
+#endif