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INSTRUCTION SET REFERENCE
FDIV/FDIVP/FIDIVDivide
Description
These instructions divide 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.
Opcode
Instruction
Description
D8 /6
FDIV m32real
Divide ST(0) by m32real and store result in ST(0)
DC /6
FDIV m64real
Divide ST(0) by m64real and store result in ST(0)
D8 F0+i
FDIV ST(0), ST(i)
Divide ST(0) by ST(i) and store result in ST(0)
DC F8+i
FDIV ST(i), ST(0)
Divide ST(i) by ST(0) and store result in ST(i)
DE F8+i
FDIVP ST(i), ST(0)Divide ST(i) by ST(0), store result in ST(i), and pop the
register stack
DE F9
FDIVP
Divide ST(1) by ST(0), store result in ST(1), and pop the
register stack
DA /6
FIDIV m32int
Divide ST(0) by m32int and store result in ST(0)
DE /6
FIDIV m16int
Divide ST(0) by m16int and store result in ST(0)
