Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1423

FDIV/FDIVP/FIDIV—Divide
Opcode
D8 /6
DC /6
D8 F0+i
DC F8+i
DE F8+i
DE F9
DA /6
DE /6
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 operands
in memory can be in single-real, double-real, word-integer, or short-integer formats.
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 real 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 extended-real format
before performing the division. When the source operand is an integer 0, it is treated as
a +0.
If an unmasked divide by zero exception (#Z) is generated, no result is stored; if the
exception is masked, an  of the appropriate sign is stored in the destination operand.
The following table shows the results obtained when dividing various classes of
numbers, assuming that neither overflow nor underflow occurs.
Volume 4: Base IA-32 Instruction Reference
Instruction Description
FDIV m32real Divide ST(0) by m32real and store result in ST(0)
FDIV m64real Divide ST(0) by m64real and store result in ST(0)
FDIV ST(0), ST( i ) Divide ST(0) by ST( i ) and store result in ST(0)
FDIV ST(i), ST(0) Divide ST( i ) by ST(0) and store result in ST( i )
FDIVP ST( i ), ST(0) Divide ST( i ) by ST(0), store result in ST( i ), and pop the register
stack
FDIVP Divide ST(1) by ST(0), store result in ST(1), and pop the
register stack
FIDIV m32int Divide ST(0) by m32int and store result in ST(0)
FIDIV m16int Divide ST(0) by m64int and store result in ST(0)
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