From: alexfrunews@nospicedham.gmail.com   
      
   On Sunday, September 13, 2020 at 11:51:13 PM UTC-7, luserdroog wrote:   
   >     // additional flags set by math operators   
   > #define MATHFLAGS *fl |= ( (z&(w?0xffff0000:0xff00))     ?CF:0) \   
   >                        | ( ((z^x)&(z^y)&(w?0x8000:0x80)) ?OF:0) \   
   >                        | ( ((x^y^z)&0x10)                ?AF:0); \   
   >                        SETPF   
   >   
   > I don't know where I came up with that expression for OF.   
   > It's gibberish to me now.   
      
   It's making sure that the result's sign is the same   
   as the signs of x and y. If that isn't true, OF gets set.   
   That works for addition, z = x + y,   
   but not subtraction, z = x - y.   
   Unless you exchange things a bit...   
      
   add: z = x + y   
   (z^x)&(z^y)&...   
      
   sub: z = x - y   
   OR, speaking in terms of addition...   
   sub: x = z + y   
   (x^z)&(x^y)&...   
      
   IOW, for the purposes of OF calculation you need to   
   exchange x and z in that formula of yours.   
      
   Alex   
      
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