libgsmhr1 RxFE: store CN R0+LPC separately from speech In the original GSM 06.06 code the ECU for speech mode is entirely separate from the CN generator, maintaining separate state. (The main intertie between them is the speech vs CN state variable, distinguishing between speech and CN BFIs, in addition to the CN-specific function of distinguishing between initial and update SIDs.) In the present RxFE implementation I initially thought that we could use the same saved_frame buffer for both ECU and CN, overwriting just the first 4 params (R0 and LPC) when a valid SID comes in. However, I now realize it was a bad idea: the original code has a corner case (long sequence of speech-mode BFIs to put the ECU in state 6, then SID and CN-mode BFIs, then a good speech frame) that would be broken by that buffer reuse approach. We could eliminate this corner case by resetting the ECU state when passing through a CN insertion period, but doing so would needlessly increase the behavioral diffs between GSM 06.06 and our version. Solution: use a separate CN-specific buffer for CN R0+LPC parameters, and match the behavior of GSM 06.06 code in this regard.

/*
 * Unfortunately the code we got from ETSI makes heavy use of two global
 * Boolean flags named Carry and Overflow that function like equally named
 * processor state flags on many CPU architectures.  They are not part
 * of persistent codec session state for either the encoder or the decoder,
 * instead they are "short-term" globals much like UNIX errno.
 *
 * Given this unfortunate reality plus the natural desire to make our
 * EFR library thread-safe (a transcoding MGW handling a large volume of
 * simultaneous calls is exactly the kind of application that would benefit
 * from utilitizing all CPU cores), our current workaround is to use
 * thread-local storage.
 */

#include <stdint.h>
#include "typedef.h"

__thread Flag EFR__Carry, EFR__Overflow;