snarkjs/src/misc.js

const _revTable = [];
for (let i=0; i<256; i++) {
    _revTable[i] = _revSlow(i, 8);
}

function _revSlow(idx, bits) {
    let res =0;
    let a = idx;
    for (let i=0; i<bits; i++) {
        res <<= 1;
        res = res | (a &1);
        a >>=1;
    }
    return res;
}

function bitReverse(idx, bits) {
    return (
        _revTable[idx >>> 24] |
        (_revTable[(idx >>> 16) & 0xFF] << 8) |
        (_revTable[(idx >>> 8) & 0xFF] << 16) |
        (_revTable[idx & 0xFF] << 24)
    ) >>> (32-bits);
}


function log2( V )
{
    return( ( ( V & 0xFFFF0000 ) !== 0 ? ( V &= 0xFFFF0000, 16 ) : 0 ) | ( ( V & 0xFF00FF00 ) !== 0 ? ( V &= 0xFF00FF00, 8 ) : 0 ) | ( ( V & 0xF0F0F0F0 ) !== 0 ? ( V &= 0xF0F0F0F0, 4 ) : 0 ) | ( ( V & 0xCCCCCCCC ) !== 0 ? ( V &= 0xCCCCCCCC, 2 ) : 0 ) | ( ( V & 0xAAAAAAAA ) !== 0 ) );
}

module.exports.bitReverse = bitReverse;
module.exports.log2 = log2;