How does CLGX CMP real # to DINT

[drbitboy]

According to the IEEE 754 standard, negative zero and positive zero should compare as equal with the usual (numerical) comparison operators, like the == operators of C and Java. In those languages, special programming tricks may be needed to distinguish the two values

Source: https://en.wikipedia.org/wiki/Signed_zero#Comparisons

 

[drbitboy]

Might explain or complement the ability to manipulate real bits directly in earlier versions of 5k - they appear here to be forcing the sign bit to zero upon detecting the signed zero value.

Maybe the opposite?

• 500 compares correctly i.e [EQU -0.0 0.0] evaluates to True
  • Even though the sign bit is 1 in the negative 0
    • See CPW of [F8:1 NEGATIVE_ZERO] to L9:2
• Logix 5000 compares incorrectly i.e. [EQU -0.0 0.0] evaluates to False