Mmix NEG和NEGU操作码

Question

根据NEG和NEGU的定义，

NEG $X,Y,$Z (negate signed): s($X) := Y - s($Z).
NEGU $X,Y,$Z (negate unsigned): u($X) := (Y - u($Z)) mod 2^64.

让我们假设$Z = s(-1)或u(2^64 - 1)。然后，第一个操作码将在Y = 0时将值1放入$X寄存器，最近的一个操作码将给出相同的结果，因为u(-(2^64 - 1)) mod 2^64 = 1。我说的对吗？$Z = -2^63时NEG指令是否应引发溢出异常

Answer 1

简短回答“当$Z =-2^63时，NEG指令是否应该引发溢出异常？”

yes, but you probably already suspected that.

从逻辑上讲，NEG $X,0，-2^63应该给出2^63，这超出了有符号正整数的界限，因此溢出。但是如果你像我一样，你想要一个整数溢出确实发生的证据。这就是它：

t       IS      $255

    LOC     #20          //handle the integer overflow event
    PUSHJ   255,Err
    PUT     rJ,$255
    GET     $255,rB
    RESUME

        LOC     #100
Main    SET     t,#4000
        PUT     rA,t        //set the integer overflow event bit
        SETH    $0,#8000
        NEG     $1,0,$0
        GETA    t,End
        TRAP    0,Fputs,StdOut
        TRAP    0,Halt,0
End     BYTE    "End of program",#a,0

Err     SET     $0,$255           //overflow subroutine, prints out message
        GETA    t,Emes
        TRAP    0,Fputs,StdOut
        GET     t,rW
        INCL    t,4
        PUT     rW,t
        SET     $255,$0
        POP     0,0
Emes    BYTE    "Error: integer overflow",#a,0