SUB

Subtract (immediate) copies a capability from the source Capability register to the destination Capability register with an optionally shifted immediate value subtracted from the value field. If the result is not representable the destination Capability register tag is cleared. If the source capability is sealed, the Capability Tag written to the destination Capability register is cleared.

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	0	0	0	0	0	1	0	1	sh	imm12												Cn					Cd
								A

SUB <Cd|CSP>, <Cn|CSP>, #<imm>{, LSL <amount>}

integer d = UInt(Cd); integer n = UInt(Cn); bits(64) imm; case sh of when '0' imm = ZeroExtend(imm12, 64); when '1' imm = ZeroExtend(imm12 : Zeros(12), 64);

Assembler Symbols

<Cd|CSP>

Is the capability name of the destination register or stack pointer, encoded in the "Cd" field.

<Cn|CSP>

Is the capability name of the source register or stack pointer, encoded in the "Cn" field.

<imm>

Is the unsigned immediate operand, in the range 0 to 4095, encoded in the "imm12" field.

Is the index shift amount, encoded in sh:

sh	<amount>
0	#0
1	#12

Operation

CheckCapabilitiesEnabled(); Capability operand1 = if n == 31 then CSP[] else C[n]; integer operand2 = UInt(imm); Capability result = CapAdd(operand1, -operand2); if CapIsSealed(operand1) then result = CapWithTagClear(result); if d == 31 then CSP[] = result; else C[d] = result;

Internal version only: isa v32.13, AdvSIMD v29.04, pseudocode morello-2022-01_rc2, capabilities morello-2022-01_rc2 ; Build timestamp: 2022-01-11T11:23