echogarden/src/encodings/Ascii.ts

An easy-to-use speech toolset. Includes tools for synthesis, recognition, alignment, speech translation, language detection, source separation and more.

import { EncodeIntoResult } from "./TextEncodingsCommon.js"

export function encodeAscii(asciiString: string) {
	const charCount = asciiString.length

	const resultArray = new Uint8Array(charCount)

	const { written } = encodeAsciiInto(asciiString, resultArray)

	return resultArray.subarray(0, written)
}

export function encodeAsciiInto(asciiString: string, resultBuffer: Uint8Array): EncodeIntoResult {
	const len = asciiString.length

	if (resultBuffer.length < len) {
		throw new Error(`Result Uint8Array is not large enough to hold the string`)
	}

	for (let readOffset = 0; readOffset < len; readOffset++) {
		const charCode = asciiString.charCodeAt(readOffset)

		if (charCode >= 128) {
			throw new Error(`Character '${asciiString[readOffset]}' (code: ${charCode}) can't be encoded as a standard ASCII character`)
		}

		resultBuffer[readOffset] = charCode
	}

	return { read: len, written: len }
}

export function decodeAscii(encodedString: Uint8Array) {
	const maxChunkLength = 2 ** 24

	const decoder = new ChunkedAsciiDecoder()

	for (let offset = 0; offset < encodedString.length; offset += maxChunkLength) {
		const chunk = encodedString.subarray(offset, offset + maxChunkLength)

		decoder.writeChunk(chunk)
	}

	return decoder.toString()
}

export class ChunkedAsciiDecoder {
	private str = ''
	private readonly textDecoder = new TextDecoder('windows-1252')

	writeChunk(chunk: Uint8Array) {
		const decodedChunk = this.textDecoder.decode(chunk, { stream: true })

		this.str += decodedChunk
	}

	toString() {
		return this.str
	}
}