;-----------------------------------------------------------------
; catu255.mu -- Microcode source for Alto running
;	64 Kilobit u-255 law coded speech.
; This code executes as part of the audio task.
; Last modified by L. Stewart September 22, 1979  5:20 PM
; October 15, 1979  2:30 PM  silence detection
; March 17, 1980  12:15 PM CAT copy, CatU255.mu
;-----------------------------------------------------------------

;-----------------------------------------------------------------
;   u-255 law encoding
;   Assumes left justified 12 bit two's complement value in L
;   u255 value returned r.j. in L and l.j. in utVal=Temp
;-----------------------------------------------------------------
!1,2,utEPlus,utEMinus;
!1,2,utEShift,utEOV;
!1,2,utEDone,utEMore;
!1,2,utEMinus1,utEPlus1;

;  First convert to sign magnitude

utEncode:	utVal_L;
	L_100000,SH<0;
	utExp_L,:utEPlus;	!1,2,utEPlus,utEMinus;

utEPlus:	L_0,TASK,:utECom1;

utEMinus:	L_0-T;
	utVal_L,T_0-1,TASK,:utECom1;

utECom1:	utSign_L,:utAddConst;

;  Now add 41B returning max on overflow
utAddConst:	T_203+1;	Lucky constant value
	L_utVal+T;
	NOP,SH<0;
	utVal _ L RSH 1,:utEShift;	!1,2,utEShift,utEOV;

utEOV:	L_177,TASK;
	utVal_L,:utEAddSign;

;  Now shift right by 2, to align the value so that it is right for the highest
;  exponent.

utEShift:	L_utVal,TASK;
	utVal _ L RSH 1;

; Now enter the main loop of the conversion.

utELoop:	T_STRCWFS;	STRCWFS=10000
	L_utVal AND T;
	L_utExp-T,SH=0;
	utExp_L,:utEDone;	!1,2,utEDone,utEMore;
utEMore:	L_utVal,TASK;
	utVal_L LSH 1,:utELoop;

; Now package everything up

utEDone:	T_7400;	4 bit mask
	T_utVal.T;
	L_utExp OR T,TASK;
	utVal_L LCY 8;

; Add in sign;
utEAddSign:
	SINK_utSign,BUS=0;
	L_T_utVal,:utEMinus1;	!1,2,utEMinus1,utEPlus1;
utEMinus1:	L_200 OR T,:utEPlus1;
utEPlus1:	utVal_L LCY 8,:utStore;

;-----------------------------------------------------------------
;   u-255 law decoding
;   Assumes right justified 8 bit u-255 value in L
;   Returns linear value in L and utVal=Temp
;-----------------------------------------------------------------
!1,2,utDLoop,utDDone;
!1,2,utDMinus,utDPlus;

utDecode:

;  First step, separate components.

	utVal_L;
	T_100;
	T_60 OR T;	Construct constant
	L_utVal AND T,TASK;
	utExp_L;

	T_utVal;
	L_200 AND T;
	utSign_L;	Minus if Sign non-zero
	L_17 AND T,TASK;
	utVal_L LSH 1;

; Build frame for decoding;
	T_utVal+1;
	L_40+T,TASK;
	utVal_L LSH 1;

;   The value is now 0 000 000 001 xxx x10 in binary.
;   We now must shift left (Exp/20B)+1 places.

utDLoop:	L_utVal,TASK;
	utVal_L LSH 1;
	T_20;
	L_utExp-T,BUS=0,TASK;
	utExp_L,:utDLoop;	!1,2,utDLoop,utDDone;

;   Now subtract 204B (see encode), this will never underflow.

utDDone:	T_203+1;
	L_utVal-T;
	T_17;
	L_LASTL AND NOT T,TASK;	Truncate towards 0.
	utVal_L;

;  Handle sign.

	SINK_utSign,BUS=0;
	L_T_utVal,:utDMinus;	!1,2,utDMinus,utDPlus;
utDMinus:	L_0-T;
utDPlus:	utVal_L,:utShipit;

;-----------------------------------------------------------------
;   u-255 law decoding
;   Assumes right justified 8 bit u-255 value in L
;   Returns linear value in L and utVal=Temp
;-----------------------------------------------------------------
!1,2,uttDLoop,uttDDone;
!1,2,uttDMinus,uttDPlus;

uttDecode:

;  First step, separate components.

	utVal_L;
	T_100;
	T_60 OR T;	Construct constant
	L_utVal AND T,TASK;
	utExp_L;

	T_utVal;
	L_200 AND T;
	utSign_L;	Minus if Sign non-zero
	L_17 AND T,TASK;
	utVal_L LSH 1;

; Build frame for decoding;
	T_utVal+1;
	L_40+T,TASK;
	utVal_L LSH 1;

;   The value is now 0 000 000 001 xxx x10 in binary.
;   We now must shift left (Exp/20B)+1 places.

uttDLoop:	L_utVal,TASK;
	utVal_L LSH 1;
	T_20;
	L_utExp-T,BUS=0,TASK;
	utExp_L,:uttDLoop;	!1,2,uttDLoop,uttDDone;

;   Now subtract 204B (see encode), this will never underflow.

uttDDone:	T_203+1;
	L_utVal-T;
	T_17;
	L_LASTL AND NOT T,TASK;	Truncate towards 0.
	utVal_L;

;  Handle sign.

	SINK_utSign,BUS=0;
	L_T_utVal,:uttDMinus;	!1,2,uttDMinus,uttDPlus;
uttDMinus:	L_0-T;
uttDPlus:	utVal_L,:uttShipit;
(0,5376)(1,11264)\f1