4.4.12 Unsigned Quadword Multiply High

Format:

UMULH

Ra.rq,Rb.rq,Rc.wq

!Operate format

UMULH

Ra.rq,#b.ib,Rc.wq

!Operate format

Operation:

Rc {Rav * U Rbv}<127:64>

Exceptions:

None

Instruction mnemonics:

UMULH

Unsigned Multiply Quadword High

Qualifiers:

None

Description:

Register Ra and Rb or a literal are multiplied as unsigned numbers to produce a 128-bit result. The high-order 64-bits are written to register Rc.

The UMULH instruction can be used to generate the upper 64 bits of a 128-bit result as follows:

Ra and Rb are unsigned: result of UMULH

Ra and Rb are signed: (result of UMULH) – Ra<63>*Rb – Rb<63>*Ra

The MULQ instruction gives the low 64 bits of the result in either case.

4–36Alpha Architecture Handbook

Page 92
Image 92
Compaq ECQD2KCTE manual Unsigned Quadword Multiply High, Umulh