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Rfft inverse transform implemented #5

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Rfft inverse transform implemented #5

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186 changes: 186 additions & 0 deletions dsp.js
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Original file line number Diff line number Diff line change
Expand Up @@ -539,6 +539,7 @@ function RFFT(bufferSize, sampleRate) {
FourierTransform.call(this, bufferSize, sampleRate);

this.trans = new Float32Array(bufferSize);
this.itrans = new Float32Array(bufferSize);

// don't use a lookup table to do the permute, use this instead
this.reverseBinPermute = function (dest, source) {
Expand Down Expand Up @@ -569,6 +570,37 @@ function RFFT(bufferSize, sampleRate) {
} while (i < halfSize);
dest[nm1] = source[nm1];
};

// don't use a lookup table to do the permute, use this instead
// the inverse transform needs to do this in place so we have this
this.reverseBinPermuteInPlace = function (buf) {
var bufferSize = this.bufferSize,
halfSize = bufferSize >>> 1,
nm1 = bufferSize - 1,
i = 1, r = 0, h, t;

do {
r += halfSize;
t = buf[i];
buf[i] = buf[r];
buf[r] = t;

i++;

h = halfSize << 1;
while (h = h >> 1, !((r ^= h) & h));

if (r >= i) {
t = buf[i];
buf[i] = buf[r];
buf[r] = t;
t = buf[nm1-i];
buf[nm1-i] = buf[nm1-r];
buf[nm1-r] = t;
}
i++;
} while (i < halfSize);
};
}


Expand All @@ -584,6 +616,11 @@ function RFFT(bufferSize, sampleRate) {
// trans[n/2+2] = im[n/2-2]
// ...
// trans[n-1] = im[1]
//
// note before using RFFT.trans you need to scale it, however since [0-1]
// is frequently not the range you want, or you often want to work with it in
// some other way we leave it unscaled for speed (this way we make one fewer
// pass, if you're willing to remeber to scale it yourself.

RFFT.prototype.forward = function(buffer) {
var n = this.bufferSize,
Expand Down Expand Up @@ -748,6 +785,8 @@ RFFT.prototype.forward = function(buffer) {
}
}

// NOTE: for extra speed we could split this step out since 'trans' is available
// however I did not since that wouldn't match the API of the others
while (--i) {
rval = x[i];
ival = x[n-i-1];
Expand All @@ -766,6 +805,153 @@ RFFT.prototype.forward = function(buffer) {
return spectrum;
};

RFFT.prototype.scale_trans() = function() {
var i=0,bSi = 1.0/n, x = this.trans;
while(i < x.length) { x[i] *= bSi; i++; }
}

// input must have ordering as in output of the forward version,
// you can just pass in this.trans and it should work (if you've scaled it)
RFFT.prototype.inverse = function(buffer) {
var n = this.bufferSize,
x = this.itrans,
TWO_PI = 2*Math.PI,
n2, n4, n8, nn,
t1, t2, t3, t4, t5,
j, i0, i1, i2, i3, i4, i5, i6, i7, i8, ud, ix, id,
st1, cc1, ss1, cc3, ss3,
e,
a;

x.set(buffer);

nn = n>>>1;
n2 = n<<1;

while ( nn >>>= 1 )
{
ix = 0;
id = n2;
n2 >>>= 1;
n4 = n2>>>2;
n8 = n4>>>1;

do // ix
{
for (i0=ix; i0<n; i0+=id)
{
i1 = i0;
i2 = i1 + n4;
i3 = i2 + n4;
i4 = i3 + n4;

//sumdiff3(x[i1], x[i3], t1);// {a, b, d} <--| {a+b, b, a-b}
t1 = x[i1] - x[i3]; x[i1] += x[i3];

x[i2] += x[i2];
x[i4] += x[i4];

//sumdiff3_r(x[i4], t1, x[i3]);// {a,b,d} <--| {a+b, b, b-a}
x[i3] = t1 - x[i4]; x[i4] += t1;

if ( n4!=1 ) // note: optimise (Note this comment from original C++)
{
i1 += n8;
i2 += n8;
i3 += n8;
i4 += n8;

//sumdiff3(x[i1], x[i2], t1); // {a, b, d} <--| {a+b, b, a-b}
t1 = x[i1] - x[i2]; x[i1] += x[i2];

//sumdiff(a, b, &s, &d) {s, d} <--| {a+b, a-b}
//sumdiff(x[i4], x[i3], t2, x[i2]);
t2 = x[i4] + x[i3]; x[i2] = x[i4] - x[i3];

t2 = -t2 * Math.SQRT2;
t1 *= Math.SQRT2;
//sumdiff(a, b, &s, &d) {s, d} <--| {a+b, a-b}
//sumdiff(t2, t1, x[i3], x[i4]);
x[i3] = t2 + t1; x[i4] = t2 - t1;
}
}

ix = (id<<1) - n2;
id <<= 2;
} while ( ix<n );

e = TWO_PI/n2;
for (j=1; j<n8; j++)
{
a = j*e;

ss1 = Math.sin(a);
cc1 = Math.cos(a);

ss3 = sin(3*a); cc3 = cos(3*a);
cc3 = 4*cc1*(cc1*cc1-0.75);
ss3 = 4*ss1*(0.75-ss1*ss1);

ix = 0;
id = n2<<1;
do // ix-loop
{
for (i0=ix; i0<n; i0+=id)
{
i1 = i0 + j;
i2 = i1 + n4;
i3 = i2 + n4;
i4 = i3 + n4;

i5 = i0 + n4 - j;
i6 = i5 + n4;
i7 = i6 + n4;
i8 = i7 + n4;

//sumdiff3(x[i1], x[i6], t1); // {a, b, d} <--| {a+b, b, a-b}
t1 = x[i1] - x[i6]; x[i1] += x[i6];
//sumdiff3(x[i5], x[i2], t2); // {a, b, d} <--| {a+b, b, a-b}
t2 = x[i5] - x[i2]; x[i5] += x[i2];
//t2 = x[i5] + x[i2]; x[i5] = x[i5] - x[i2];

//sumdiff(a, b, &s, &d) {s, d} <--| {a+b, a-b}
//sumdiff(x[i8], x[i3], t3, x[i6]);
//sumdiff(x[i4], x[i7], t4, x[i2]);
t3 = x[i8] + x[i3]; x[i6] = x[i8] - x[i3];
t4 = x[i4] + x[i7]; x[i2] = x[i4] - x[i7];

//sumdiff3(t1, t4, t5); // {a, b, d} <--| {a+b, b, a-b}
t5 = t1 - t4; t1 += t4;
//sumdiff3(t2, t3, t4); // {a, b, d} <--| {a+b, b, a-b}
t4 = t2 - t3; t2 += t3;

//cmult(c, s, x, y, &u, &v) {u,v} <--| {x*c-y*s, x*s+y*c}
//cmult(ss1, cc1, t5, t4, x[i7], x[i3]);
//cmult(cc3, ss3, t1, t2, x[i4], x[i8]);
x[i7] = t5*ss1 - t4*cc1; x[i3] = t5*cc1 + t4*ss1;
x[i4] = t1*cc3 - t2*ss3; x[i8] = t1*ss3 + t2*cc3;
}

ix = (id<<1) - n2;
id <<= 2;
} while ( ix < n );
}
}

for (ix=0, id=4; ix<n; id*=4)
{
for (i0=ix; i0<n; i0+=id) {
// sumdiff(&a, &b) {a, b} <--| {a+b, a-b}
//sumdiff(x[i0], x[i0+1]);
st1 = x[i0] - x[i0+1]; x[i0] += x[i0+1]; x[i0+1] = st1;
}
ix = 2*(id-1);
}

this.reverseBinPermuteInPlace(x);
return x;
};

function Sampler(file, bufferSize, sampleRate, playStart, playEnd, loopStart, loopEnd, loopMode) {
this.file = file;
this.bufferSize = bufferSize;
Expand Down