Hello Chen,
I don't see why you assume BIT4 to be a signed char. I think it already is
an int. But yes, after ~ it will certainly be an int.
Maarten
> Hi All,
>
> I have the following code below, with "default" signed char type.
>
> -----------
> #define BIT4 0b00010000
> #define P_IO_Ctrl_Base 0x2080
>
> #define P_IO_PortC_Data *(volatile unsigned char *) (P_IO_Ctrl_Base+0x1A)
>
> #define DrvGPIO_SetBit(GPIO,BITIO) GPIO |= BITIO;
> #define DrvGPIO_ClrBit(GPIO,BITIO) GPIO &= ~BITIO;
>
> void main()
> {
> DrvGPIO_ClrBit(P_IO_PortC_Data,BIT4);
> }
> ----------
>
> I add `--fverbose-asm` option to see more details on the codegen. What
> I'm curious about is the code snipt below:
>
> ----------
> ld a,(#0x209A)
> ; peephole 17 loaded a from (#0x209A) directly instead of using hl.
> ; genCast
> ; genAnd
> and a, #0xEF
> ---------
>
> Although the genCast doesn't emit code, I am wondering why we need a
> casting here. So I study C integer conversion rules [1] a little bit,
> and here is my reasoning.
>
> 1. BIT4 => signed char
>
> 2. ~BIT4 => int
>
> 3. and we now have the following situation,
>
> P_IO_PortC_Data &= ~BIT4
> ^^^^^^^^^^^^^^^ ^^^^^
>
> unsigned char int
>
> | *
> v
>
> int
>
> the reason we have genCast is because we have unsigned char to int
> promotion.
>
> Am I right or wrong about the C integer conversion rules? :-)
>
> Thanks in advance.
>
> [1]
> https://www.securecoding.cert.org/confluence/display/seccode/INT02-C.+Understand+integer+conversion+rules
>
>
> Regards,
> chenwj
>
> --
> Wei-Ren Chen (é³éä»»)
> Homepage: http://people.cs.nctu.edu.tw/~chenwj
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