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