User Guide

280 x87 Floating-Point Programming

AMD64 Technology 24592—Rev. 3.15—November 2009

determines that an unmasked exception is pending—by checking the exception status (ES) flag in the

x87 status word—and invokes the #MF exception service routine.

#MF Exception Types and Flags. The #MF exceptions are of six types, five of which are mandated

by the IEEE 754 standard. These six types and their bit-flags in the x87 status word are shown in

Table 6-17. A stack fault (SF) exception is always accompanied by an invalid-operation exception

(IE). A summary of each exception type is given in “x87 Status Word Register (FSW)” on page 241.

The sections below describe the causes for the #MF exceptions. Masked and unmasked responses to

the exceptions are described in “x87 Floating-Point Exception Masking” on page 283. The priority of

#MF exceptions are described in “x87 Floating-Point Exception Priority” on page 282.

Invalid-Operation Exception (IE). The IE exception occurs due to one of the attempted operations

shown in Table 6-18 on page 281. An IE exception may also be accompanied by a stack fault (SF)

exception. See “Stack Fault (SF)” on page 282.

Table 6-17. x87 Floating-Point (#MF) Exception Flags

Exception and Mnemonic

x87 Status-

Word Bit

Comparable IEEE 754

Exception

Invalid-operation exception (IE) 0 Invalid Operation

Invalid-operation exception (IE)

with stack fault (SF) exception

0 and 6 none

Denormalized-operand exception (DE) 1 none

Zero-divide exception (ZE) 2 Division by Zero

Overflow exception (OE) 3 Overflow

Underflow exception (UE) 4 Underflow

Precision exception (PE) 5 Inexact

Note:

1. See “x87 Status Word Register (FSW)” on page 241 for a summary of each exception.