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A compilation problem

wfy1008

In my codes, I got a strange result following. I compilerd by C51 9.03, and C51 9.60 is as the same result. That doesn't fit my logic. In the comment after the code is the value obtained when debugging

unsigned char aa,bb,cc,dd;
aa = 0xab;
bb = 0xcd;
cc = (aa+bb)%255;    //cc=0x79
dd = (unsigned char)((aa+bb)%255);  //dd=0x78

The following  is the disassembly code. The right is the option of C51.

In fact, cc and dd should be 0x79. I use parentheses to clearly indicate the operation priority order: first calculate the sum, calculate the modulus, and then cast to unsigned char.

I tried in VC2010, TI CCS3.3, both can get the correct result 0x79, that is to say, cc=0x79 and dd=0x79.

Thank you for your attention.

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