lifehash/src/lifehash/BitEnumerator.js

TypeScript/JavaScript implementation of LifeHash, a visual hash algorithm

export class BitEnumerator {
    constructor(data) {
        this.data = data;
        this.index = 0;
        this.mask = 128;
    }
    has_next() {
        return this.mask !== 0 || this.index !== this.data.length - 1;
    }
    next() {
        if (!this.has_next()) {
            throw new Error('BitEnumerator underflow.');
        }
        if (this.mask === 0) {
            this.mask = 128;
            this.index += 1;
        }
        const b = (this.data[this.index] & this.mask) !== 0;
        this.mask >>= 1;
        return b;
    }
    next_configurable(bitMask, bits) {
        let val = 0;
        let m = bitMask;
        for (let i = 0; i < bits; i += 1) {
            if (this.next()) {
                val |= m;
            }
            m >>= 1;
        }
        return val;
    }
    next_uint2() {
        return this.next_configurable(2, 2);
    }
    next_uint8() {
        return this.next_configurable(128, 8);
    }
    next_uint16() {
        return this.next_configurable(32768, 16);
    }
    next_frac() {
        return this.next_uint16() / 65535.0;
    }
}