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9- 18 M68040 USER’S MANUAL MOTOROLA
particularly careful of the lack of trichotomy in the floating-point branches since it is
common for compilers to invert the sense of conditions.
When using the IEEE nonaware tests, the user receives a BSUN exception whenever a
branch is attempted and the NAN condition code bit is set, unless the branch is an FBEQ
or an FBNE. If the BSUN exception is enabled in the FPCR, the exception causes another
exception. Therefore, the IEEE nonaware program is interrupted if an unexpected
condition occurs. Compilers and programmers who are knowledgeable of the IEEE 754
standard should use the IEEE aware tests in programs that contain ordered and
unordered conditions. Since the ordered or unordered attribute is explicitly included in the
conditional test, the BSUN bit is not set in the FPSR EXC byte when the unordered
condition occurs. Table 9-8 summarizes the conditional mnemonics, definitions,
equations, predicates, and whether the BSUN bit is set in the FPSR EXC byte for the 32
floating-point conditional tests. The equation column lists the combination of FPCC bits for
each test in the form of an equation.
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