public byte[] encode(byte[] pcmIn)
{
byte[] Output;
Output = new byte[(pcmIn.Length) / 4 + 3];
uint i;
short s;
int sign; // Current adpcm sign bit
int delta; // Current adpcm output value
int step; // Stepsize
int valprev; // virtual previous output value
int vpdiff; // Current change to valprev
int index; // Current step change index
byte bitbuffer = 0; // place to keep previous 4-bit value
valprev = this.s.valprev;
index = this.s.index;
step = stepsizeTable[index];
for (i = 0; i <= pcmIn.Length - 4; i += 4)
{
s = BitConverter.ToInt16(pcmIn, (int)i);
//**** Step 1 - compute difference with previous value
delta = s - valprev;
sign = (delta < 0) ? 8 : 0;
if (sign == 8)
{
delta = -delta;
}
//**** Step 2 - Divide and clamp
delta = (int)Math.Round((double)(delta << 2) / (double)step);
if (delta > 7)
{
delta = 7;
}
vpdiff = (delta * step) >> 2;
//**** Step 3 - Update previous value
if (sign == 8)
{
valprev -= vpdiff;
}
else
{
valprev += vpdiff;
}
//**** Step 4 - Clamp previous value to 16 bits
if (valprev > short.MaxValue)
{
valprev = short.MaxValue;
}
else if (valprev < short.MinValue)
{
valprev = short.MinValue;
}
//**** Step 5 - Assemble value, update index and step values
delta = delta | sign;
index += indexTable[delta];
if (index < 0)
{
index = 0;
}
if (index > 88)
{
index = 88;
}
step = stepsizeTable[index];
//**** Step 6 - Writing values into the array
bitbuffer = (byte)(delta << 4);
//NEXT SAMPLE
s = BitConverter.ToInt16(pcmIn, (int)i + 2);
//**** Step 1 - compute difference with previous value
delta = s - valprev;
sign = (delta < 0) ? 8 : 0;
if (sign == 8)
{
delta = -delta;
}
//**** Step 2 - Divide and clamp
delta = (int)Math.Round((double)(delta << 2) / (double)step);
if (delta > 7)
{
delta = 7;
}
vpdiff = (delta * step) >> 2;
//**** Step 3 - Update previous value
if (sign == 8)
{
valprev -= vpdiff;
}
else
{
valprev += vpdiff;
}
//**** Step 4 - Clamp previous value to 16 bits
if (valprev > short.MaxValue)
{
valprev = short.MaxValue;
}
else if (valprev < short.MinValue)
{
valprev = short.MinValue;
}
//**** Step 5 - Assemble value, update index and step values
delta = delta | sign;
index += indexTable[delta];
if (index < 0)
{
index = 0;
}
if (index > 88)
{
index = 88;
}
step = stepsizeTable[index];
//**** Step 6 - Writing values into the array
Output[i / 4 + 3] = (byte)(delta | bitbuffer);
}
//Splitting Values to Byte-Array
Output[0] = BitConverter.GetBytes(this.s.valprev)[0];
Output[1] = BitConverter.GetBytes(this.s.valprev)[1];
Output[2] = this.s.index;
//Update state
this.s.valprev = (short)valprev;
this.s.index = (byte)index;
//Output
return(Output);
}
public void resetState()
{
s = new StateMono();
}
