PRB: 8087 mnemonics without Operators (11339)
The information in this article applies to:
- Microsoft Macro Assembler (MASM) 1.25
- Microsoft Macro Assembler (MASM) 5.0
- Microsoft Macro Assembler (MASM) 5.1
- Microsoft Macro Assembler (MASM) 6.0
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.
| Modification Type: | Minor | Last Reviewed: | 10/13/2003 |
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| Keywords: | KB11339 |
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