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const FIRST_BIT = 0x80;
const FIRST_TWO_BITS = 0xc0;
const FIRST_THREE_BITS = 0xe0;
const FIRST_FOUR_BITS = 0xf0;
const FIRST_FIVE_BITS = 0xf8;
const TWO_BIT_CHAR = 0xc0;
const THREE_BIT_CHAR = 0xe0;
const FOUR_BIT_CHAR = 0xf0;
const CONTINUING_CHAR = 0x80;
/**
* Determines if the passed in bytes are valid utf8
* @param bytes - An array of 8-bit bytes. Must be indexable and have length property
* @param start - The index to start validating
* @param end - The index to end validating
*/
export function validateUtf8(
bytes: { [index: number]: number },
start: number,
end: number
): boolean {
let continuation = 0;
for (let i = start; i < end; i += 1) {
const byte = bytes[i];
if (continuation) {
if ((byte & FIRST_TWO_BITS) !== CONTINUING_CHAR) {
return false;
}
continuation -= 1;
} else if (byte & FIRST_BIT) {
if ((byte & FIRST_THREE_BITS) === TWO_BIT_CHAR) {
continuation = 1;
} else if ((byte & FIRST_FOUR_BITS) === THREE_BIT_CHAR) {
continuation = 2;
} else if ((byte & FIRST_FIVE_BITS) === FOUR_BIT_CHAR) {
continuation = 3;
} else {
return false;
}
}
}
return !continuation;
}
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