ADPCM Matlab Code

Hi There,
I have been searching for the Matlab code for 40, 32, 24, 16 KBits/s
ADPCM code (G.726) for the last one week but could not find a good
working/ compliant code. Can anyone tell me where to get free version
of the ADPCM code in Matlab compliant to the G.726 standard?

Thanks,

Farhan