I think Keil C51 version 8 has a bug in the code generation. The following source shows the bug:
typedef unsigned char BYTE; typedef unsigned short WORD; #define FIXED_VAULE 64 #define MAKEWORD(h, l) (((WORD )(h) << 8) | (BYTE )(l)) void main(void) { BYTE x = 2; BYTE y = 2; WORD z; // The code generation for this line is incorrect z = MAKEWORD(FIXED_VAULE - x - 1, FIXED_VAULE - y - 1); // The Keil v8 asm listing shows the generated code for this // line is different to the previous line's. z = MAKEWORD(FIXED_VAULE - 1 - x, FIXED_VAULE - 1 - y); // However, if MAKEWORD is defined as: // #define MAKEWORD(h, l) (((WORD )(h) << 8) | (WORD )(l)) // the ASM code for 2 lines are the same. }