jianpuAlgo.js

function jianpu_to_pitch(jianpu) {
    const pitch_steps = [0, 1, 2, 3, 4, 5, 6]
    const code = []
    const dur = []
    let du_type = 0
    let du_dots = 0
    let du_mul = 0
    let du = 0
    // remove lyrics line
    jianpu = jianpu.split('\n')
        .filter(line => !line.startsWith('L:') && !line.startsWith('ｂｐｍ'))
        .join('\n');
    for (var i = 0; i < jianpu.length; i++) {
        let ch = jianpu[i]
        if (ch == '/') {
            do {
                i++
                ch = jianpu[i]
            } while (/[A-Za-z0-9]/.test(ch)) ;
            if (ch == '(') {
                do {
                    i++
                    ch = jianpu[i]
                } while (ch && ch != ')' && ch != '\n') ;
            }
        }
        if ('1' <= ch && ch <= '7') {
            let pitch = pitch_steps[ch.charCodeAt(0) - 49]
            if (i > 0) {
                ch = jianpu[i-1]
                /*if (ch == '#') {
                    pitch += 1
                    if (i > 1 && jianpu[i-2] == '#')
                        pitch += 1
                }
                else if (ch == 'b') {
                    pitch -= 1
                    if (i > 1 && jianpu[i-2] == 'b')
                        pitch -= 1
                }*/
            }
            code.push(pitch % 12)
            du += 0.5**du_type * (2 - 0.5**du_dots) * (du_mul+1)
            dur.push(du)
            du_type = du_dots = du_mul = du = 0
        }
        else if (ch == '0' || ch == '-') {
            du += 0.5**du_type * (2 - 0.5**du_dots) * (du_mul+1)
            du_type = du_dots = du_mul = 0
        }
        else if (ch == '_')
            du_type += 1
        else if (ch == '=')
            du_type += 2
        else if (ch == '.')
            du_dots += 1
        else if (ch == '-')
            du_mul += 1
    }
    du += 0.5**du_type * (2 - 0.5**du_dots) * (du_mul+1)
    dur.push(du);
    return {pitch: code, duration: dur.slice(1)}
}

function match_score(song, query, song_dur) {
    const ns = song.length, nq = query.length
    if (ns == 0 || nq == 0)
        return [999999, 0, 0];
    let dp1 = new Float64Array(ns+1)
    let dp2 = new Float64Array(ns+1)
    let bt1 = new Int32Array(ns+1)
    let bt2 = new Int32Array(ns+1)
    const avg = song_dur.reduce((p, v) => p+v, 0) / ns
    // Try to match begin of music phrase
    for (var i = 1; i < ns; i++)
        dp1[i] = Math.max(1.2 - song_dur[i-1] / avg, 0) * 2
    for (var i = 0; i <= ns; i++)
        bt1[i] = i;
    dp1[ns] = 999999
    for (var i = 0; i < nq; i++) {
        dp2[0] = 999999
        for (var j = 0; j < ns; j++) {
            let diff = Math.abs(song[j] - query[i])
            if (diff > 3) diff = 7 - diff
            let nxt = Math.min(dp1[j] + diff, dp1[j+1] + 2, dp2[j] + 2)
            dp2[j+1] = nxt;
            if (dp2[j] + 2 == nxt)
                bt2[j+1] = bt2[j];
            else if (dp1[j] + diff == nxt)
                bt2[j+1] = bt1[j];
            else
                bt2[j+1] = bt1[j+1];
        }
        [dp1, dp2] = [dp2, dp1];
        [bt1, bt2] = [bt2, bt1]
    }
    // No need to match end of music phrase
    //for (var i = 0; i < ns; i++)
    //    dp1[i+1] += Math.max(1.2 - song_dur[i] / avg, 0) * 2
    let best = dp1.reduce((p, v) => Math.min(p, v), 999999)
    let from = 0, to = 0;
    for (var i = 0; i <= ns; i++) {
        if (dp1[i] == best) {
            from = bt1[i];
            to = i;
            break;
        }
    }
    return [best, from, to];
}

module.exports = {jianpu_to_pitch, match_score};