{
	A-Law compression routine.

	Calling Parameters
    R0 = Linear Input Value

	Result Registers
    R0 = Compressed 8-bit value

	Altered Registers
    R0, R1, R13, R15;

	Cycles Time
    20 Cycles

    Version 0.01    8/10/90	Gordon A. Sterling
}

#include "asm_glob.h"

.SEGMENT/PM	Assembly_Library_Code_Space;

.GLOBAL	    acompress;

acompress:	R15=ABS R0;			{Take absolute value}
		R13=4095;			{Maximum PCM value}
		R15=MIN(R15,R13);		{Cap input}
		R1=LSHIFT R15 BY -1;		{Prepare for possible zero seg}
		R13=31;				{Check for zero segment}
		COMP(R15,R13);
		IF LE JUMP sign_invert;		{Append sign and invert bits}

		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}
		R1=26;
		R13=R1-R13, R1=R15;		{Compute segment}
		R1=R1 OR LSHIFT R13 BY 4;	{Position segment bits}

sign_invert:	R0=PASS R0;			{Append the sign bit and invert}
		IF GE R1=BSET R1 BY 7;
		RTS (DB);
		R13=H#55;
		R0=R1 XOR R13;			{Invert bits}

.ENDSEG;