umulh

Unsigned Multiply High

UMULH <Xd>, <Xn>, <Xm>

Multiplies two 64-bit registers, keeps high 64 bits (Unsigned).

Details

Multiplies the unsigned 64-bit values in Xn and Xm, treating both as unsigned integers, and stores the high 64 bits of the 128-bit product in Xd. This is AArch64-only. No arithmetic flags are affected.

Pseudocode Operation

temp ← Xn × Xm; Xd ← temp[127:64]

Example

UMULH x0, x1, x2

Encoding

Binary Layout
1
00
11011
1
10
Rm
0
11111
Rn
Rd
 
Format Data Processing
Opcode 0x9BC07C00
Extension Base

Operands

  • Xd
    Destination 64-bit integer register
  • Xn
    First source / base 64-bit integer register
  • Xm
    Second source / offset 64-bit integer register

Reference (Arm A64 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x9BC07C00 UMULH <Xd>, <Xn>, <Xm> A64 1 | 00 | 11011 | 1 | 10 | Rm | 0 | 11111 | Rn | Rd
0x04130000 UMULH <Zdn>.<T>, <Pg>/M, <Zdn>.<T>, <Zm>.<T> A64 00000100 | size | 0100 | 1 | 1 | 000 | Pg | Zm | Zdn
0x04206C00 UMULH <Zd>.<T>, <Zn>.<T>, <Zm>.<T> A64 00000100 | size | 1 | Zm | 0110 | 1 | 1 | Zn | Zd

Description

Unsigned Multiply High multiplies two 64-bit register values, and writes bits[127:64] of the 128-bit result to the 64-bit destination register.

Operation

bits(64) operand1 = X[n, 64];
bits(64) operand2 = X[m, 64];

integer result;

result = Int(operand1, TRUE) * Int(operand2, TRUE);

X[d, 64] = result<127:64>;