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Fdiv/fdivp/fidiv-divide, Fdiv/fdivp/fidiv—divide – Intel 253666-024US User Manual

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3-316 Vol. 2A

FDIV/FDIVP/FIDIV—Divide

INSTRUCTION SET REFERENCE, A-M

FDIV/FDIVP/FIDIV—Divide

Description

Divides the destination operand by the source operand and stores the result in the
destination location. The destination operand (dividend) is always in an FPU register;
the source operand (divisor) can be a register or a memory location. Source oper-
ands in memory can be in single-precision or double-precision floating-point format,
word or doubleword integer format.
The no-operand version of the instruction divides the contents of the ST(1) register
by the contents of the ST(0) register. The one-operand version divides the contents
of the ST(0) register by the contents of a memory location (either a floating-point or
an integer value). The two-operand version, divides the contents of the ST(0)
register by the contents of the ST(i) register or vice versa.
The FDIVP instructions perform the additional operation of popping the FPU register
stack after storing the result. 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 divide instructions always results in the register
stack being popped. In some assemblers, the mnemonic for this instruction is FDIV
rather than FDIVP.
The FIDIV instructions convert an integer source operand to double extended-preci-
sion floating-point format before performing the division. When the source operand
is an integer 0, it is treated as a +0.

Opcode

Instruction

64-Bit

Mode

Compat/

Leg Mode

Description

D8 /6

FDIV m32fp

Valid

Valid

Divide ST(0) by m32fp and store

result in ST(0).

DC /6

FDIV m64fp

Valid

Valid

Divide ST(0) by m64fp and store

result in ST(0).

D8 F0+i

FDIV ST(0), ST(i)

Valid

Valid

Divide ST(0) by ST(i) and store result

in ST(0).

DC F8+i

FDIV ST(i), ST(0)

Valid

Valid

Divide ST(i) by ST(0) and store result

in ST(i).

DE F8+i

FDIVP ST(i), ST(0)

Valid

Valid

Divide ST(i) by ST(0), store result in

ST(i), and pop the register stack.

DE F9

FDIVP

Valid

Valid

Divide ST(1) by ST(0), store result in

ST(1), and pop the register stack.

DA /6

FIDIV m32int

Valid

Valid

Divide ST(0) by m32int and store

result in ST(0).

DE /6

FIDIV m16int

Valid

Valid

Divide ST(0) by m64int and store

result in ST(0).