162 lines
3.9 KiB
C
162 lines
3.9 KiB
C
#include "tape.h"
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#include "common.h"
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#include <stdlib.h>
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#include <memory.h>
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#include <string.h>
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unsigned reads = 0;
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unsigned writes = 0;
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void _tape_load_block(tape_t* tape, unsigned n);
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void _tape_flush(tape_t* tape);
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tape_t* tape_open(const char* filename, const char* mode)
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{
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FILE* file = fopen(filename, mode);
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printfv(VERBOSITY_VERBOSE, "Opening tape %s in mode %s.\n", filename, mode);
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if (!file) {
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fprintf(stderr, "Cannot open %s in %s mode.", filename, mode);
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return NULL;
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}
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tape_t* tape = malloc(sizeof(tape_t));
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tape->file = file;
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tape->mode = mode;
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tape->name = malloc(strlen(filename));
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tape->buffer = malloc(PAGE_SIZE);
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strcpy(tape->name, filename);
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if (strcmp(mode, TAPE_READ) == 0) {
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tape->read = 0;
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tape->offset = 0;
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tape->block = -1;
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} else if (strcmp(mode, TAPE_WRITE) == 0) {
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tape->read = 0;
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tape->offset = 0;
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tape->block = 0;
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} else if (strcmp(mode, TAPE_APPEND) == 0) {
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size_t pos = ftell(tape->file);
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tape->offset = pos % PAGE_SIZE;
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tape->block = pos / PAGE_SIZE;
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_tape_load_block(tape, tape->block);
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} else {
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fprintf(stderr, "Mode %s is unknown for tapes.", mode);
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}
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return tape;
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}
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void tape_close(tape_t* tape)
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{
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printfv(VERBOSITY_VERBOSE, "Closing tape %s.\n", tape->name);
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if (strcmp(tape->mode, TAPE_WRITE) == 0 || strcmp(tape->mode, TAPE_APPEND) == 0) {
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_tape_flush(tape);
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}
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fclose(tape->file);
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free(tape->name);
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free(tape->buffer);
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free(tape);
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}
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void _tape_load_block(tape_t* tape, unsigned n)
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{
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printfv(VERBOSITY_DEBUG, "Loading block %u of %s.\n", n, tape->name);
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fseek(tape->file, n * PAGE_SIZE, SEEK_SET);
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tape->offset = 0;
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tape->read = fread(tape->buffer, 1, PAGE_SIZE, tape->file);
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tape->block = n;
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reads++;
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}
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void _tape_flush(tape_t* tape)
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{
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if (tape->offset == 0) {
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return;
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}
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printfv(VERBOSITY_DEBUG, "Flushing block %d (%u bytes) of %s.\n", tape->block, tape->offset, tape->name);
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fseek(tape->file, tape->block * PAGE_SIZE, SEEK_SET);
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fwrite(tape->buffer, 1, tape->offset, tape->file);
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tape->offset = 0;
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tape->block++;
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writes++;
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}
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void* tape_read(tape_t* tape, void* record, size_t size)
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{
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if (tape->offset >= tape->read) {
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// load next block
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_tape_load_block(tape, tape->block + 1);
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}
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if (tape->offset + size > tape->read && feof(tape->file)) {
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return NULL;
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}
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if (tape->offset + size > tape->read) {
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size_t rest = tape->read - tape->offset;
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memcpy(record, tape->buffer + tape->offset, rest);
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_tape_load_block(tape, tape->block + 1);
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memcpy(record + rest, tape->buffer + tape->offset, size - rest);
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// move tape offset
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tape->offset += size - rest;
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} else {
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memcpy(record, tape->buffer + tape->offset, size);
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tape->offset += size;
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}
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return record;
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}
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int tape_rewind(tape_t* tape, size_t n, size_t size)
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{
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int bytes = n * size;
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int take = tape->offset < bytes ? tape->offset : bytes;
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bytes -= take;
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tape->offset -= take;
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while (bytes > 0) {
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_tape_load_block(tape, tape->block - 1);
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bytes -= PAGE_SIZE;
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}
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tape->offset -= bytes;
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return tape->block;
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}
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int tape_write(tape_t* tape, void* record, size_t size)
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{
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size_t written = 0;
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while (tape->offset + size > PAGE_SIZE) {
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size_t available = PAGE_SIZE - tape->offset;
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memcpy(tape->buffer + tape->offset, record + written, available);
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tape->offset += available;
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size -= available;
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written += available;
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_tape_flush(tape);
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}
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if (size) {
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memcpy(tape->buffer + tape->offset, record + written, size);
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tape->offset += size;
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written += size;
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}
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return written;
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}
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