Tried with:
avr-gcc (GCC) 3.4.6 (Gentoo 3.4.6-r2 p1.5, ssp-3.4.6-1.0, pie-8.7.10)
avr-gcc (GCC) 4.2.4 (Gentoo 4.2.4 p1.0)
avr-gcc (Gentoo 4.3.2-r2 p1.5, pie-10.1.5) 4.3.2
Both -Os and -O0 behave the same, the -mmcu=atmega1281 and -mmcu=atmega128 too
(however the later was not tested on all 6 combinations)
When the complex statement is replaced with the commented out equivalent, the
result is right. It fails on stated magic numbers - the code is basically a
test if a write to external memory crosses the 64KB chip boundary or not.
Complete source code:
#define F_CPU 16000000UL
#include <avr/io.h>
uint8_t _eeprom_cross16bit( uint32_t a, uint16_t c ) {
/*
uint32_t s = a & 0x10000;
uint32_t e = (a + c -1) & 0x10000;
return s != e;
*/
return (a & 010000) != ( (a + c -1) & 010000 );
}
// main code
int main(void) {
// init LEDS
PORTC = 0;
DDRC = 0xFF;
// comparison result:
if (_eeprom_cross16bit( 4075 , 43 )) {
// wrong
PORTC = 0x55;
} else {
// good
PORTC = 0x0F;
}
while(1);
return 0;
}
--
Summary: [avr] Complex equations evaluate wrong
Product: gcc
Version: 3.4.6
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: daniel at rozsnyo dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38767
