77 lines
2.4 KiB
TypeScript
77 lines
2.4 KiB
TypeScript
import { word } from 'js/types';
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import { ProDOSVolume } from '.';
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import type { VDH } from './vdh';
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const BLOCK_ENTRIES = 4096;
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export class BitMap {
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private vdh: VDH;
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private blocks: Uint8Array[];
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constructor(volume: ProDOSVolume) {
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this.vdh = volume.vdh();
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this.blocks = volume.blocks();
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}
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freeBlocks() {
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const free: word[] = [];
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let blockOffset = 0;
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let byteOffset = 0;
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let bitOffset = 0;
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let bitMapBlock = this.blocks[this.vdh.bitMapPointer + blockOffset];
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for (let idx = 0; idx < this.vdh.totalBlocks; idx++) {
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const currentByte = bitMapBlock[byteOffset];
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const mask = 1 << bitOffset;
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if (currentByte & mask) {
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free.push(idx);
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}
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bitOffset += 1;
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if (bitOffset > 7) {
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bitOffset = 0;
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byteOffset += 1;
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if (byteOffset > BLOCK_ENTRIES >> 3) {
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byteOffset = 0;
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blockOffset += 1;
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bitMapBlock =
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this.blocks[this.vdh.bitMapPointer + blockOffset];
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}
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}
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}
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return free;
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}
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allocBlock() {
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for (let idx = 0; idx < this.vdh.totalBlocks; idx++) {
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const blockOffset = Math.floor(idx / BLOCK_ENTRIES);
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const bitMapBlock =
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this.blocks[this.vdh.bitMapPointer + blockOffset];
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const byteOffset = (idx - blockOffset * BLOCK_ENTRIES) >> 8;
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const bits = bitMapBlock[byteOffset];
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if (bits !== 0xff) {
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let mask = 0x01;
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for (let bitOffset = 0; bitOffset < 8; bitOffset++) {
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if (!(bits & mask)) {
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bitMapBlock[byteOffset] |= mask;
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return idx;
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}
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mask <<= 1;
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}
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}
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}
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throw new Error('Disk full');
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}
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freeBlock(block: word) {
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if (block >= this.vdh.totalBlocks) {
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throw new Error('Block out of range');
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}
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const blockOffset = Math.floor(block / BLOCK_ENTRIES);
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const byteOffset = (block - blockOffset * BLOCK_ENTRIES) >> 8;
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const bitOffset = block & 0x7;
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const bitMapBlock = this.blocks[this.vdh.bitMapPointer + blockOffset];
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bitMapBlock[byteOffset] &= 0xff ^ (0x01 << bitOffset);
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}
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}
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