js/src/util/bit.ts

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

import { TypedArray } from '../type';

export function align(value: number, alignment: number) {
    return value + padding(value, alignment);
}

export function padding(value: number, alignment: number) {
    return (value % alignment === 0 ? 0 : alignment - value % alignment);
}

export function getBool(_data: any, _index: number, byte: number, bit: number) {
    return (byte & 1 << bit) !== 0;
}

export function getBit(_data: any, _index: number, byte: number, bit: number): 0 | 1 {
    return (byte & 1 << bit) >> bit as (0 | 1);
}

export function setBool(bytes: Uint8Array, index: number, value: any) {
    return value ?
        !!(bytes[index >> 3] |=  (1 << (index % 8))) || true :
        !(bytes[index >> 3] &= ~(1 << (index % 8))) && false ;
}

export function packBools(values: Iterable<any>) {
    let n = 0, i = 0;
    let xs: number[] = [];
    let bit = 0, byte = 0;
    for (const value of values) {
        value && (byte |= 1 << bit);
        if (++bit === 8) {
            xs[i++] = byte;
            byte = bit = 0;
        }
    }
    if (i === 0 || bit > 0) { xs[i++] = byte; }
    if (i % 8 && (n = i + 8 - i % 8)) {
        do { xs[i] = 0; } while (++i < n);
    }
    return new Uint8Array(xs);
}

export function* iterateBits<T>(bytes: Uint8Array, begin: number, length: number, context: any,
                                get: (context: any, index: number, byte: number, bit: number) => T) {
    let bit = begin % 8;
    let byteIndex = begin >> 3;
    let index = 0, remaining = length;
    for (; remaining > 0; bit = 0) {
        let byte = bytes[byteIndex++];
        do {
            yield get(context, index++, byte, bit);
        } while (--remaining > 0 && ++bit < 8);
    }
}

/**
 * Compute the population count (the number of bits set to 1) for a range of bits in a Uint8Array.
 * @param vector The Uint8Array of bits for which to compute the population count.
 * @param lhs The range's left-hand side (or start) bit
 * @param rhs The range's right-hand side (or end) bit
 */
export function popcnt_bit_range(data: Uint8Array, lhs: number, rhs: number): number {
    if (rhs - lhs <= 0) { return 0; }
    // If the bit range is less than one byte, sum the 1 bits in the bit range
    if (rhs - lhs < 8) {
        let sum = 0;
        for (const bit of iterateBits(data, lhs, rhs - lhs, data, getBit)) {
            sum += bit;
        }
        return sum;
    }
    // Get the next lowest multiple of 8 from the right hand side
    const rhsInside = rhs >> 3 << 3;
    // Get the next highest multiple of 8 from the left hand side
    const lhsInside = lhs + (lhs % 8 === 0 ? 0 : 8 - lhs % 8);
    return (
        // Get the popcnt of bits between the left hand side, and the next highest multiple of 8
        popcnt_bit_range(data, lhs, lhsInside) +
        // Get the popcnt of bits between the right hand side, and the next lowest multiple of 8
        popcnt_bit_range(data, rhsInside, rhs) +
        // Get the popcnt of all bits between the left and right hand sides' multiples of 8
        popcnt_array(data, lhsInside >> 3, (rhsInside - lhsInside) >> 3)
    );
}

export function popcnt_array(arr: TypedArray, byteOffset?: number, byteLength?: number) {
    let cnt = 0, pos = byteOffset! | 0;
    const view = new DataView(arr.buffer, arr.byteOffset, arr.byteLength);
    const len =  byteLength === void 0 ? arr.byteLength : pos + byteLength;
    while (len - pos >= 4) {
        cnt += popcnt_uint32(view.getUint32(pos));
        pos += 4;
    }
    while (len - pos >= 2) {
        cnt += popcnt_uint32(view.getUint16(pos));
        pos += 2;
    }
    while (len - pos >= 1) {
        cnt += popcnt_uint32(view.getUint8(pos));
        pos += 1;
    }
    return cnt;
}

export function popcnt_uint32(uint32: number): number {
    let i = uint32 | 0;
    i = i - ((i >>> 1) & 0x55555555);
    i = (i & 0x33333333) + ((i >>> 2) & 0x33333333);
    return (((i + (i >>> 4)) & 0x0F0F0F0F) * 0x01010101) >>> 24;
}