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3-320 Vol. 2A FDIVR/FDIVRP/FIDIVR—Reverse Divide
INSTRUCTION SET REFERENCE, A-M
FDIVR/FDIVRP/FIDIVR—Reverse Divide
Description
Divides the source operand by the destination operand and stores the result in the
destination location. The destination operand (divisor) is always in an FPU register;
the source operand (dividend) 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.
These instructions perform the reverse operations of the FDIV, FDIVP, and FIDIV
instructions. They are provided to support more efficient coding.
The no-operand version of the instruction divides the contents of the ST(0) register
by the contents of the ST(1) register. The one-operand version divides the contents
of a memory location (either a floating-point or an integer value) by the contents of
the ST(0) register. The two-operand version, divides the contents of the ST(i)
register by the contents of the ST(0) register or vice versa.
The FDIVRP 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 FDIVR
rather than FDIVRP.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
D8 /7 FDIVR m32fp Valid Valid Divide m32fp by ST(0) and store result
in ST(0).
DC /7 FDIVR m64fp Valid Valid Divide m64fp by ST(0) and store result
in ST(0).
D8 F8+i FDIVR ST(0), ST(i) Valid Valid Divide ST(i) by ST(0) and store result in
ST(0).
DC F0+i FDIVR ST(i), ST(0) Valid Valid Divide ST(0) by ST(i) and store result in
ST(i).
DE F0+i FDIVRP ST(i), ST(0) Valid Valid Divide ST(0) by ST(i), store result in
ST(i), and pop the register stack.
DE F1 FDIVRP Valid Valid Divide ST(0) by ST(1), store result in
ST(1), and pop the register stack.
DA /7 FIDIVR m32int Valid Valid Divide m32int by ST(0) and store result
in ST(0).
DE /7 FIDIVR m16int Valid Valid Divide m16int by ST(0) and store result
in ST(0).