From f0e550345e353813875b5b5d4d9ea7e3d5a77bae Mon Sep 17 00:00:00 2001
From: Gentoo <installgentoo@endianness.com>
Date: Fri, 4 Dec 2020 12:46:34 +1100
Subject: initial commit

---
 Makefile | 12 +++++++++++
 main.c   | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 Makefile
 create mode 100644 main.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..6d5f37a
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,12 @@
+CC=gcc
+CFLAGS=-O3 -march=native -pipe
+
+OBJ = main.o
+
+%.o: %.c $(DEPS)
+	$(CC) -c -o $@ $< $(CFLAGS)
+
+gct-generate: $(OBJ)
+	$(CC) -o $@ $^ $(CFLAGS)
+clean:
+	rm gct-generate main.o
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..8e19b51
--- /dev/null
+++ b/main.c
@@ -0,0 +1,69 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+	if (argc < 2){fprintf(stderr,"Usage: %s <codes.txt>\n", argv[0]); exit(1);}
+
+	FILE *output = fopen("output.gct","wb");
+	if (!output){fprintf(stderr,"Could not open output file!\n"); exit(1);}
+
+	/* Header */
+	char header[] = {0x00,0xd0,0xc0,0xde,0x00,0xd0,0xc0,0xde};
+	fwrite(header, 1, 8, output);
+
+	FILE *input = fopen(argv[1],"r");
+	if (!input){fprintf(stderr,"Could not open:%s!\n",argv[1]); exit(1);}
+
+	/* check that the given file isn't empty */
+	fseek(input, 0L, SEEK_END);
+	if (!ftell(input)){fprintf(stderr,"File %s is empty.\n", argv[1]); exit(1);}
+	rewind(input);
+
+	char code[18];
+	size_t result;
+
+	/* convert each ASCII encoded hex line into the byte values and write that to the gct file */
+	while ((result = fread(code, 1, 18, input)))
+		{
+		if (result < 18){fprintf(stderr, "Invalid code length.\n"); exit(1);}
+
+		/* remove space in middle of code line */
+		for (int i = 8; i < 17; ++i)
+			{
+			code[i] = code[i+1];
+			}
+
+		/* convert ASCII encoded hex to byte values */
+		for (int i = 0, j = 0; i < 8; ++i, j += 2)
+			{
+			int amount0;
+			int amount1;
+
+			/* check if first number is decimal or hex */
+			if (code[j] >= '0' && code[j] <= '9'){amount0 = '0';}
+			else if (code[j] >= 'A' && code[j] <= 'F') {amount0 = 55;}
+			else {fprintf(stderr,"Invalid code character: %c\n", code[j]); exit(1);}
+
+			/* check if second number is decimal or hex */
+			if (code[j+1] >= '0' && code[j+1] <= '9'){amount1 = '0';}
+			else if (code[j+1] >= 'A' && code[j+1] <= 'F') {amount1 = 55;}
+			else {fprintf(stderr,"Invalid code character: %c\n", code[j+1]); exit(1);}
+
+			/* extract the two characters and place them into one byte */
+			code[i] = ((code[j] - amount0) << 4) | (code[j+1] - amount1);
+			}
+
+		/* write the code to the gct file */
+		fwrite(code, 1, 8, output);
+		}
+
+
+	/* Footer */
+	char footer[] = {0xf0,0,0,0,0,0,0,0};
+	fwrite(footer, 1, 8, output);
+
+	fclose(output);
+	fclose(input);
+        return 0;
+}
-- 
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