Microsoft KB Archive/11339

= PRB: 8087 mnemonics without Operators =

Article ID: 11339

Article Last Modified on 10/13/2003

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APPLIES TO


 * Microsoft Macro Assembler 1.25
 * Microsoft Macro Assembler 5.0
 * Microsoft Macro Assembler 5.1 Standard Edition
 * Microsoft Macro Assembler 6.0 Standard Edition

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This article was previously published under Q11339



SYMPTOMS
When assembled with no operands, the 8087 instructions FADD, FDIV, FDIVR, FMUL, FSUB, and FSUBR assemble as if they were the instructions "FADDP ST(1),ST", "FDIVP ST(1),ST", and so forth.



CAUSE
The assembler is correct. When used with no operands, these instructions perform "classical stack" operations.



MORE INFORMATION
The following is from Pages 6-23 of the "Intel iAPX 86/88, 186/188 User's Manual Programmer's Reference":

The classical stack form may be used to make the 8087 operate like a classical stack machine. No operands are coded in this form, only the instruction mnemonic. The NDP (8087) picks the source operand from the stack top and the destination from the next stack element. It then pops the stack, performs the operation, and returns the result to the new stack top, effectively replacing the operands by the result.

Note: FADD, FSUB, FMUL, and FDIV also pop if no operands are specified, in spite of the fact that the mnemonics do not have P as a last character.

A similar passage can be found on Pages 2-5 of the Numeric Supplement to the "iAPX 286 Programmer's Reference" manual.

Additional query words: 1.25 5.00 5.10 6.00

Keywords: KB11339

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