{	    

	Mu-Law Compression routine.	

	Calling Parameters
    R0 = Linear input value

	Result Registers
    R0 = Compressed 8-bit value

	Altered Registers
    R0, R13, R15

	Cycle Time
    19 Cycles

    The Applications Library
    Gordon A. Sterling  3/20/90

}

#include "asm_glob.h"

.SEGMENT/PM   Assembly_Library_Code_Space;

.GLOBAL	ucompress;

ucompress:	R15=ABS R0;			{Take absolute value}
		R13=33;				{Add offset of boundries}
		R15=R15+R13;
		R13=8191;			{Maximum PCM value}
		R15=MIN(R15,R13);		{Cap input}
		R13=EXP R15;			{Find exponent adjustment}
		R13=-R13;
		R15=ASHIFT R15 BY R13;		{Normalize input}
		R15=BCLR R15 BY 30;	   	{Remove first significant bit}
		R15=LSHIFT R15 BY -26;		{Shift position bits}
		R0=PASS R0;			{Test sign of input}
		IF LT R15=BSET R15 BY 7;	{Set sign bit if necessary}
		R0=25;
		R0=R0-R13;			{Compute segment}
		IF LT R0=R0-R0;
		R15=R15 OR LSHIFT R0 BY 4;	{Position segment bits}
		RTS (DB);
		R13=H#FF;
		R0=R15 XOR R13;			{Invert bits}

.ENDSEG;