day1

.gitignore

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+input*
+part1*
+part2*

Makefile

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+
+DAYS= day1
+
+.PHONY: all
+
+day%/part2: day%
+	cd $< && $(MAKE)
+
+all: $(addsuffix /part2,$(DAYS))
+		

day1/Makefile

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+
+OPT_FLAGS?= -march=native -fgraphite -fopenmp -floop-parallelize-all -ftree-parallelize-loops=4 \
+	    -floop-interchange -ftree-loop-distribution -floop-strip-mine -floop-block \
+	    -fno-stack-check -fno-strict-aliasing
+
+.PHONY: all
+all: part1 part2
+
+.PHONY: big
+big: part1-big part2-big
+
+input.h: input
+	@rm -f $@
+	while read line; do \
+		echo "$$line," >> $@; \
+	done < $<
+
+input-big.h: input-big
+	@rm -f $@
+	while read line; do \
+		echo "$${line}ul," >> $@; \
+	done < $<
+
+
+part1: input.h
+	gcc day1.c -O3 -flto $(OPT_FLAGS) -o $@ -O3 -flto
+	strip $@
+
+part2: input.h
+	gcc day1.c -DPART2 -O3 -flto $(OPT_FLAGS) -o $@ -O3 -flto
+	strip $@
+
+part1-big: input-big.h
+	gcc day1.c -DBIG -O3 -flto $(OPT_FLAGS) -o $@ -O3 -flto
+	strip $@
+
+part2-big: input-big.h
+	gcc day1.c -DBIG -DPART2 -O3 -flto $(OPT_FLAGS) -o $@ -O3 -flto
+	strip $@
+
+clean:
+	rm -f part{1,2}
+	rm -f input.h

day1/day1.c

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+#include <stddef.h>
+#include <stdio.h>
+
+typedef unsigned long u64;
+
+#ifdef BIG
+#define TARGET 99920044
+#else
+#define TARGET 2020
+#endif
+
+const u64 input[] = {
+#ifdef BIG
+#include "input-big.h"
+#else
+#include "input.h"
+#endif
+};
+const size_t input_sz = sizeof(input)/sizeof(u64);
+
+int main()
+{
+	for(register u64 i=0;i<input_sz;i++)
+		for(register u64 j=i;j<input_sz;j++)
+#ifdef PART2
+			for(register u64 k=j;k<input_sz;k++)
+				if(input[i] + input[j] + input[k] == TARGET)
+				{
+					printf("%lu\n", input[i] * input[j] * input[k]);
+					return 0;
+				}
+#else
+			if (input[i] + input[j] == TARGET)
+			{
+				printf("%lu\n", input[i] * input[j]);
+				return 0;
+			}
+#endif
+	return 1;
+}