50 lines
1.5 KiB
TypeScript
50 lines
1.5 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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allocBlock () {
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for (let idx = 0; idx < this.vdh.totalBlocks; idx++) {
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const blockOffset = this.vdh.bitMapPointer + Math.floor(idx / BLOCK_ENTRIES);
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const bitMapBlock = this.blocks[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 = this.vdh.bitMapPointer + 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[blockOffset];
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bitMapBlock[byteOffset] &= 0xff ^ (0x01 << bitOffset);
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}
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}
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