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/*
!!DESCRIPTION!!
!!ORIGIN!! testsuite
!!LICENCE!! Public Domain
!!AUTHOR!! Marc 'BlackJack' Rintsch
*/
/*
Compiler is build from cc65-snapshot-2.13.9.20101031 sources.
Expected results and also what I get from this without any optimisations
are: 48663 and 49218
When I turn on ''-O'': 58096 and 58096. After swapping the two variable
declaration lines in 'calculate_checksum()' the results are correct
with ''-O''.
But with ''--O --static-locals'' the results are incorrect again (31757
and 15408). ''--static-locals'' alone works though.
*/
#include <stdio.h>
#include <stdint.h>
// uint16_t __fastcall__ calculate_checksum(uint8_t *block);
uint8_t block[256];
uint16_t calculate_checksum(uint8_t *block)
{
uint16_t i, result = 0xffff;
uint8_t j;
for (i = 0; i < 256; ++i) {
result ^= block[i] << 8;
for (j = 0; j < 8; ++j) {
if (result & (1 << 15)) {
result = (result << 1) ^ 0x1021;
} else {
result <<= 1;
}
}
}
return ~result;
}
int main(void)
{
uint16_t i;
printf("zeroes: %u\n", calculate_checksum(block));
for (i = 0; i < 256; ++i) block[i] = i;
printf("0..255: %u\n", calculate_checksum(block));
return 0;
}
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