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Vol. 2A 3-351
INSTRUCTION SET REFERENCE, A-M
FMUL/FMULP/FIMUL—Multiply
FMUL/FMULP/FIMUL—Multiply
Description
Multiplies the destination and source operands and stores the product in the destina-
tion location. The destination operand is always an FPU data register; the source
operand can be an FPU data register or a memory location. Source operands in
memory can be in single-precision or double-precision floating-point format or in
word or doubleword integer format.
The no-operand version of the instruction multiplies the contents of the ST(1)
register by the contents of the ST(0) register and stores the product in the ST(1)
register. The one-operand version multiplies the contents of the ST(0) register by the
contents of a memory location (either a floating point or an integer value) and stores
the product in the ST(0) register. The two-operand version, multiplies the contents of
the ST(0) register by the contents of the ST(i) register, or vice versa, with the result
being stored in the register specified with the first operand (the destination
operand).
The FMULP instructions perform the additional operation of popping the FPU register
stack after storing the product. To pop the register stack, the processor marks the
ST(0) register as empty and increments the stack pointer (TOP) by 1. The no-
operand version of the floating-point multiply instructions always results in the
register stack being popped. In some assemblers, the mnemonic for this instruction
is FMUL rather than FMULP.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
D8 /1 FMUL m32fp Valid Valid Multiply ST(0) by m32fp and store
result in ST(0).
DC /1 FMUL m64fp Valid Valid Multiply ST(0) by m64fp and store
result in ST(0).
D8 C8+i FMUL ST(0), ST(i) Valid Valid Multiply ST(0) by ST(i) and store result
in ST(0).
DC C8+i FMUL ST(i), ST(0) Valid Valid Multiply ST(i) by ST(0) and store result
in ST(i).
DE C8+i FMULP ST(i), ST(0) Valid Valid Multiply ST(i) by ST(0), store result in
ST(i), and pop the register stack.
DE C9 FMULP Valid Valid Multiply ST(1) by ST(0), store result in
ST(1), and pop the register stack.
DA /1 FIMUL m32int Valid Valid Multiply ST(0) by m32int and store
result in ST(0).
DE /1 FIMUL m16int Valid Valid Multiply ST(0) by m16int and store
result in ST(0).