Initial commit of project!

LICENSE

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+MIT License
+
+Copyright (c) 2024 A.M. Rowsell
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

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+APP=main
+AWK=awk
+CC=gcc
+CFLAGS=-std=gnu11 -O2
+
+SRCS     = $(wildcard *.c)
+OBJS     = $(SRCS:.c=.o)
+
+.PHONY: all clean
+
+all: clean $(APP) plot
+
+$(APP): $(OBJS)
+	$(CC) $(LDFLAGS) $^ $(LIBS) -o $@
+
+clean:
+	$(RM) $(OBJS) $(APP) plot.png
+
+plot: $(APP)
+	./$(APP) $(TAPS) | $(AWK) -v k=0 '{ print k " " $$1; k++ }' > 16bit.txt
+	gnuplot plot
+	xdg-open plot.png

main.c

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+#include <stdlib.h>
+#include <stdio.h>
+#include <inttypes.h>
+#include <stddef.h>
+
+// x^16 + x^15 + x^13 + x^1 + 1 -- D4 LFSR
+// 0, 7, 12, 14 works for 16-bits
+// 1, 12, 14, 15 works for 16-bits
+// 16,14,13,11
+// 0, 12, 14, 15 works for 15-bits
+// 31, 9, 7, 6, 3, 2
+// 29, 28, 25, 24, 22, 0
+// 0x8000019F
+
+void createGnuplot(int tap1, int tap2, int tap3, int tap4) {
+	char buf[1] = " ";
+	FILE *template = fopen("plottemplate", "r");
+	FILE *plotout = fopen("plot", "w");
+	if(template == NULL || plotout == NULL) {
+		return;
+	}
+	while(1) {
+		*buf = fgetc(template);
+		if (*buf == EOF) {
+			fflush(plotout);
+			break;
+		}
+		if(*buf == '$') {
+			fprintf(plotout, "%d, %d, %d, %d", tap1, tap2, tap3, tap4);
+		} else {
+			fputc(*buf, plotout);
+		}
+	}
+	fclose(template);
+	fclose(plotout);
+
+	return;
+}
+
+int main(int argc, char **argv) {
+	uint16_t startState = 0x0005;
+	uint16_t lfsr = startState;
+	uint16_t bit;
+	uint32_t count = 0;
+	char *c;
+	int tap1, tap2, tap3, tap4;
+
+
+	if(argc == 5) {
+		tap1 = strtol(argv[1], NULL, 10);
+		tap2 = strtol(argv[2], NULL, 10);
+		tap3 = strtol(argv[3], NULL, 10);
+		tap4 = strtol(argv[4], NULL, 10);
+	} else {
+		tap1 = 15;
+		tap2 = 4;
+		tap3 = 2;
+		tap4 = 1;
+	}
+	//printf("Initial state: %0x\n", lfsr);
+
+	do {
+		bit = ((lfsr >> tap1) ^ (lfsr >> tap2) ^ (lfsr >> tap3) ^ (lfsr >> tap4));
+		lfsr = (lfsr >> 1) | (bit << 15);
+		count++;
+		//count % 100000000 == 0 ? printf("0x%08x\t%032b\n", lfsr, lfsr) : 0; // comment this line for speed check
+        printf("%d\n", lfsr);
+        // *c = scanf("%s");
+	} while(lfsr != startState && count < 70000); //while(lfsr != startState);
+	//printf("Final count: %u\n", count);
+	createGnuplot(tap1, tap2, tap3, tap4);
+
+	return 0;
+}

plottemplate

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+set border linewidth 5
+
+set style line 101 lt 0 lc rgb "gray20" lw 0.5
+set style line 102 lt 2 lc rgb "black" lw 1
+
+set xlabel 'Sequence number'
+set ylabel 'LFSR value'
+
+set ytics 2500
+set mytics 2
+set xrange [0:65535]
+set yrange [0:65535]
+set xtics 2500 rotate by 60 right
+set mxtics 2
+set tics scale 1
+
+set title "16-bit LFSR: Taps $"
+
+set terminal png size 3840,2160 font 'Fira Code Nerd Font,30'
+set output "plot.png"
+plot "16bit.txt" using 1:2 notitle with points lc 14 pt 6 ps 0.5