MSUBPT

Multiply-subtract checked pointer

This instruction multiplies two register values, subtracts the product from a third register value, and writes the result to the destination register. The intermediate product is treated as the offset.

If the operation would have generated a result where the most significant 8 bits of the result register differ from the most significant 8 bits of the base register, then the result is modified such that it is likely to be non-canonical when used as an address.

If the intermediate product cannot be correctly represented as a 64-bit two's complement value, then the result is modified such that it is likely to be non-canonical when used as an address.

Integer class

(FEAT_CPA)

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
1	0	0	1	1	0	1	1	0	1	1	Rm					1	Ra					Rn					Rd
sf	op54							op31								o0

Encoding

MSUBPT <Xd>, <Xn>, <Xm>, <Xa>

Decode

if !IsFeatureImplemented(FEAT_CPA) then EndOfDecode(Decode_UNDEF); end; let d : integer{} = UInt(Rd); let n : integer{} = UInt(Rn); let m : integer{} = UInt(Rm); let a : integer{} = UInt(Ra);

Assembler Symbols

<Xd>	Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Xn>	Is the 64-bit name of the first general-purpose source register holding the multiplicand, encoded in the "Rn" field.

<Xm>	Is the 64-bit name of the second general-purpose source register holding the multiplier, encoded in the "Rm" field.

<Xa>	Is the 64-bit name of the third general-purpose source register holding the minuend, encoded in the "Ra" field.

Operation

let operand1 : bits(64) = X{}(n); let operand2 : bits(64) = X{}(m); let operand3 : bits(64) = X{}(a); var result : bits(64); let product : integer = SInt(operand1) * SInt(operand2); // Signed and unsigned twos complement arithmetic are equivalent if only a // fixed number of bits are considered. result = operand3 - product[63:0]; let overflow : boolean = (product != SInt(product[63:0])); result = PointerMultiplyAddCheck(result, operand3, overflow); X{64}(d) = result;