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Re: [avr-gcc-list] Warning message

From: Gre7g Luterman
Subject: Re: [avr-gcc-list] Warning message
Date: Tue, 2 Oct 2007 23:23:55 -0700 (PDT)

--- Royce Pereira <address@hidden> wrote:

> What does the following warning mean?
> warning: comparison is always true due to limited
> range of data type

It means the if will always happen.

> #define CHK_1307      0x55

> uint8 twi_read(void)

>       if(twi_read() != ~CHK_1307) ok= 0;

CHK_1307 = 0x55
~CHK_1307 = 0xFFAA
Since twi_read returns a byte, it will never be 0xFFAA
so the if will always happen.

Try casting it back to a byte:

if (twi_read() != ((uint8_t) ~CHK_1307)) ok = 0;


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