SRISC5 CPU

R-Format		I-Format		code	description
signed	unsigned	signed	unsigned
cmpeq		cmpeqi		==	a equals b
cmpne		cmpnei		!=	a not equal to b
cmplt	cmpltu	cmplti	cmpltui	<	a less than b
cmpgt	cmpgtu	cmpgti	cmpgtui	>	a greater than b
cmple	cmpleu	cmplei	cmpleui	<=	a not greater than b
cmpge	cmpgeu	cmpgei	cmpgeui	>=	a not less than b

pseudo-instruction

cmplt rC, rA, rB		if (signed) rA < (signed) rB then rC ← 1 else rC ← 0
cmplti rB, rA, IMM16		if (signed) rA < (signed) se(IMM16) then rB ← 1 else rB ← 0
cmpltu rC, rA, rB		if (unsigned) rA < (unsigned) rB then rC ← 1 else rC ← 0
cmpltui rB, rA, IMM16		if (unsigned) rA < (unsigned) {0x0000, IMM16} then rB ← 1 else rB ← 0

control	inst	code	description
00	cmpeq	==	a equals b
01	cmpne	!=	a not equal to b
10	cmplt	<	a less than b
11	cmpge	>=	a not less than b

Set ALU control for either signed subtraction (001) or unsigned subtraction (011), depending on the value of control[2]. Then check the status of the result:

cmp = (control[1]? neg: zero)^control[0];

control[2]? unsigned: signed

control[4:0]	operation
00xxx	ALU operations
010xx	compare, signed
011xx	compare, unsigned
10xxx	shift
11xxx	shift - immediate

control[4:3] is the data multiplexer control.