CBB<cc>

Compare bytes and branch

This instruction compares the byte values in two registers, and conditionally branches to a label at a PC-relative offset if the condition is true. This instruction provides a hint that this is not a subroutine call or return. This instruction does not affect the condition flags.

This instruction is used by the pseudo-instructions CBBLE, CBBLO, CBBLS, and CBBLT.

Branch class

(FEAT_CMPBR)

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	1	1	1	0	1	0	0	cc			Rm					1	0	imm9									Rt
																	H

Greater than encoding

(cc == 000)

CBBGT <Wt>, <Wm>, <label>

Greater than or equal encoding

(cc == 001)

CBBGE <Wt>, <Wm>, <label>

Higher encoding

(cc == 010)

CBBHI <Wt>, <Wm>, <label>

Higher or same encoding

(cc == 011)

CBBHS <Wt>, <Wm>, <label>

Equal encoding

(cc == 110)

CBBEQ <Wt>, <Wm>, <label>

Not equal encoding

(cc == 111)

CBBNE <Wt>, <Wm>, <label>

Decode (all encodings)

if !IsFeatureImplemented(FEAT_CMPBR) then EndOfDecode(Decode_UNDEF); end; let datasize : integer{} = 8 << UInt(H); let t : integer = UInt(Rt); let m : integer = UInt(Rm); let offset : bits(64) = SignExtend{}(imm9::'00'); var op : CmpOp; var unsigned : boolean; case cc of when '000' => op = Cmp_GT; unsigned = FALSE; when '001' => op = Cmp_GE; unsigned = FALSE; when '010' => op = Cmp_GT; unsigned = TRUE; when '011' => op = Cmp_GE; unsigned = TRUE; when '110' => op = Cmp_EQ; unsigned = TRUE; when '111' => op = Cmp_NE; unsigned = TRUE; otherwise => EndOfDecode(Decode_UNDEF); end;

Assembler Symbols

<Wt>	Is the 32-bit name of the general-purpose register to be tested, encoded in the "Rt" field.

<Wm>	Is the 32-bit name of the second general-purpose source register, encoded in the "Rm" field.

<label>

Is the program label to be conditionally branched to. Its offset from the address of this instruction, in the range -1024 to 1020, is encoded as "imm9" times 4.

Operation

let operand1 : bits(datasize) = X{}(t); let operand2 : bits(datasize) = X{}(m); let branch_conditional : boolean = TRUE; let value1 : integer = if unsigned then UInt(operand1) else SInt(operand1); let value2 : integer = if unsigned then UInt(operand2) else SInt(operand2); var cond : boolean; case op of when Cmp_EQ => cond = value1 == value2; when Cmp_NE => cond = value1 != value2; when Cmp_GE => cond = value1 >= value2; when Cmp_GT => cond = value1 > value2; end; if cond then BranchTo{64}(PC64() + offset, BranchType_DIR, branch_conditional); else BranchNotTaken(BranchType_DIR, branch_conditional); end;

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