[libre-riscv-dev] [Bug 279] New: inconsistency in 3.0B spec on definition of "equivalence" operator

[bugzilla-daemon@libre-riscv.org]

http://bugs.libre-riscv.org/show_bug.cgi?id=279

            Bug ID: 279
           Summary: inconsistency in 3.0B spec on definition of
                    "equivalence" operator
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: Specification
          Assignee: lkcl@lkcl.net
          Reporter: lkcl@lkcl.net
                CC: libre-riscv-dev@lists.libre-riscv.org
   NLnet milestone: ---

Section 1.3.4 p6

Equivalence logical operators ((a===b) = (a XOR ¬b))

Section 2.5.1 p40

The bit in the Condition Register specified by BA+32 is
XORed with the bit in the Condition Register specified
by BB+32, and the complemented result is placed into
the bit in the Condition Register specified by BT+32.

Section 3.3.13 p95

The contents of register RS are XORed with the con-
tents of register RB and the complemented result is
placed into register RA.

these are "technically" equivalent, however the definition is inconsistent
with the wording.  to be consistent, Section 1.3.4 should read:

Equivalence logical operators ((a===b) = ¬(a XOR b))

however by an accidental property of XOR, they're the same.

also known as an "XNOR gate", which is *sigh* a better name than "Equivalence"
https://en.wikipedia.org/wiki/XNOR_gate

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