56 lines
1.1 KiB
C
56 lines
1.1 KiB
C
//
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// Example for a 16-bit NFLSR
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//
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#include <stdio.h>
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#include <stdint.h>
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#include <string.h>
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#define LFSR_SIZE 16
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#define DEFAULT_START_STATE 0xACE1 // Default initial state for NLFSR
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uint16_t lfsr;
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uint8_t used[65535];
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uint8_t non_linear_feedback(uint16_t state) {
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// Example non-linear function: XOR of specific bits and AND of others
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uint8_t bit1 = (state >> 0) & 1;
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uint8_t bit2 = (state >> 2) & 1;
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uint8_t bit3 = (state >> 3) & 1;
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uint8_t bit4 = (state >> 5) & 1;
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uint8_t bit5 = (state >> 9) & 1;
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return (bit1 ^ bit2 ^ bit3 ^ bit4 ^ bit5);
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}
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uint8_t clock_and_shift_lfsr() {
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uint8_t ret = lfsr & 1;
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uint8_t new_bit = non_linear_feedback(lfsr);
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lfsr = (lfsr >> 1) | (new_bit << (LFSR_SIZE - 1));
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return ret;
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}
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int main() {
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uint16_t input;
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uint16_t cycle = 0;
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memset(used, sizeof(used), 0);
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printf("Enter IV for LFSR: "); scanf("%hd", &input);
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input = input & 0xFFFF;
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lfsr = input;
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while (1) {
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cycle++;
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printf("%d", clock_and_shift_lfsr());
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if (used[lfsr] > 0)
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break;
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else
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used[lfsr] = 1;
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// printf("%d\n", nlfsr);
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}
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printf("\nCycle length: %d bits.\n", cycle);
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return 0;
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}
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