From: NoOne@nospicedham.NoWhere.com   
      
   On 9/13/2020 11:13 PM, luserdroog wrote:   
   > I'm trying to fill out my toy forth interpreter and I think I have   
   > a bug in my emulator for the CMP instruction and therefore probably   
   > also SUB and SBB.   
   >   
   > The problem is showing up in my comparator functions   
   > CODE(<,     less,      POP(CX),POP(BX), MOVAXI(0xff,0xff), CMP(,R,BX,CX),   
   JL,2,INC_(R,AX), PUSH(AX))   
   > CODE(>,     more,      POP(CX),POP(BX), MOVAXI(0xff,0xff), CMP(,R,BX,CX),   
   JG,2,INC_(R,AX), PUSH(AX))   
   >   
   > When I test it with   
   >   
   > WORD(test2a,test2a,    enter, one, ten, less, dot,   
   >                                one, ten, more, dot, ok)   
   >   
   > no matter how I permute the arguments -- changing BX and CX in the CMP   
   > instruction, or in the POP order, or in the test script -- the results   
   > never change.   
   >   
   >    0 -1 OK   
   >   
   > Here's the stack trace on the first one.   
   >   
   > ax:ffff cx:000a dx:0000 bx:0001 sp:f000 bp:1ffc si:0e1a di:0000 ip:046d   
   fl:0004 NC NO NS NZ   
   > 3b(073) cmpwt: d9(331) x:1 y:10 ->fffffff7   
   > ax:ffff cx:000a dx:0000 bx:0001 sp:f000 bp:1ffc si:0e1a di:0000 ip:046f   
   fl:0891 CA OV SN NZ   
   > 7c(174) jl: 02(002) <0>   
   > ax:ffff cx:000a dx:0000 bx:0001 sp:f000 bp:1ffc si:0e1a di:0000 ip:0471   
   fl:0891 CA OV SN NZ   
   > ff(377) grp2w: c0(300) INC ->0000   
   >   
   > The CMP produces fffffff7 which seems like the correct subtraction   
   > extended to 32 bits. But the JL isn't taken.   
   >   
   > Are my flags wrong after the cmpwt instruction?   
   >   
      
   This is a real "emu"   
   https://i.insider.com/5d31dff836e03c28ef338ee2?width=1300&format=jpeg&auto=webp   
      
   --   
   Copyright 2020 Pete Olcott   
      
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