image-size/dist/esm/utils/bit-reader.js

get dimensions of any image file

export class BitReader {
    input;
    endianness;
    byteOffset = 2;
    bitOffset = 0;
    constructor(input, endianness) {
        this.input = input;
        this.endianness = endianness;
    }
    getBits(length = 1) {
        let result = 0;
        let bitsRead = 0;
        while (bitsRead < length) {
            if (this.byteOffset >= this.input.length) {
                throw new Error('Reached end of input');
            }
            const currentByte = this.input[this.byteOffset];
            const bitsLeft = 8 - this.bitOffset;
            const bitsToRead = Math.min(length - bitsRead, bitsLeft);
            if (this.endianness === 'little-endian') {
                const mask = (1 << bitsToRead) - 1;
                const bits = (currentByte >> this.bitOffset) & mask;
                result |= bits << bitsRead;
            }
            else {
                const mask = ((1 << bitsToRead) - 1) << (8 - this.bitOffset - bitsToRead);
                const bits = (currentByte & mask) >> (8 - this.bitOffset - bitsToRead);
                result = (result << bitsToRead) | bits;
            }
            bitsRead += bitsToRead;
            this.bitOffset += bitsToRead;
            if (this.bitOffset === 8) {
                this.byteOffset++;
                this.bitOffset = 0;
            }
        }
        return result;
    }
}