Initial commit

Makefile

@@ -0,0 +1,47 @@
+name := ovldec
+
+dir_source := source
+dir_build := build
+
+CFLAGS := -O0 -g -Wall -Wextra -std=c17 $(CFLAGS)
+
+CFLAGS += #$(shell pkg-config --cflags ...)
+LDLIBS += #$(shell pkg-config --libs ...)
+
+SANIT := -fsanitize=address -fsanitize=pointer-compare -fsanitize=pointer-subtract -fsanitize=leak -fsanitize=undefined
+OPTIM := -Os -fdata-sections -ffunction-sections -flto -fuse-linker-plugin -fipa-pta -Wl,--gc-sections -Wl,--print-gc-sections -fgraphite-identity -floop-nest-optimize
+
+rwildcard = $(foreach d, $(wildcard $1*), $(filter $(subst *, %, $2), $d) $(call rwildcard, $d/, $2))
+objects := $(patsubst $(dir_source)/%.c, $(dir_build)/%.o, $(call rwildcard, $(dir_source)/, *.c))
+
+.SECONDEXPANSION:
+
+.PHONY: all
+all: $(name)
+
+.PHONY: clean
+clean:
+	rm -rf $(dir_build) $(name)
+
+.PHONY: sanit
+sanit: CFLAGS += $(SANIT)
+sanit: LDFLAGS += $(SANIT)
+sanit: $(name)
+
+.PHONY: optim
+optim: CFLAGS += $(OPTIM)
+optim: LDFLAGS += $(OPTIM)
+optim: $(name)
+	strip --strip-all --strip-unneeded $(name)
+
+$(name): $(objects)
+	$(LINK.o) $^ $(LOADLIBES) $(LDLIBS) -o $@
+
+$(dir_build)/%.o: $(dir_source)/%.c | $$(dir $$@)
+	$(COMPILE.c) -MMD -MF $(@:.o=.d) $(OUTPUT_OPTION) $<
+
+.PRECIOUS: %/
+%/:
+	mkdir -p $@
+
+-include $(patsubst %.o, %.d, $(objects))

source/main.c

@@ -0,0 +1,149 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+// This is a LZ77-esque compression algorithm.
+// However, unlike LZ77, it decompresses itself in-place.
+// This is done by storing and reading the compressed data _backwards_,
+//   and writing the decompressed data far beyond the end of the compressed blob.
+// Of course, that's not a *requirement* of any sort.
+void nitro_decompress(void *header)
+{
+    if (!header) return;
+
+    unsigned dest_offset = *((uint32_t *)header - 1);
+    unsigned data_offset = *((uint32_t *)header - 2) >> 24;
+    unsigned end_offset = *((uint32_t *)header - 2) & 0xFFFFFF;
+
+    // Compressed size: end_offset
+    // Header + padding size: data_offset
+    // Decompressed size: dest_offset + end_offset + 1
+
+    uint8_t *dest = (uint8_t *)header + dest_offset;
+    uint8_t *data = (uint8_t *)header - data_offset;
+    uint8_t *end = (uint8_t *)header - end_offset;
+
+    while (data > end) {
+        uint8_t flags = *--data;
+
+        for (int i = 8; i > 0; i--) {
+            if (flags & 0x80) {
+                unsigned length = ((*(data - 1) & 0xF0) >> 4) + 3;
+                unsigned offset = (((*(data - 1) & 0x0F) << 8) | *(data - 2)) + 2;
+                data -= 2;
+
+                for (unsigned x = length; x > 0; x--) {
+                    char d = *(dest + offset);
+                    *--dest = d;
+                }
+            } else {
+                *--dest = *--data;
+            }
+            flags <<= 1;
+            if (data <= end) break;
+        }
+    }
+
+    return;
+}
+
+void usage(const char *prgname)
+{
+    fprintf(stderr, "Usage: %s [-o offset] [--] <in> <out>\n", prgname);
+    exit(1);
+}
+
+int main(int argc, char *argv[])
+{
+    FILE *f;
+    int argi = 1;
+
+    int offset = 0;
+
+    for (;;) {
+        if (argc <= argi) usage(argv[0]);
+        if (argv[argi][0] != '-') break;
+
+        if (strcmp(argv[argi], "--") == 0) {
+            argi++;
+            break;
+        } else if (strcmp(argv[argi], "-o") == 0) {
+            if (argc <= argi + 1) {
+                fprintf(stderr, "-o: Missing offset\n");
+                usage(argv[0]);
+            }
+            offset = strtol(argv[argi + 1], NULL, 0);
+            argi += 2;
+        } else {
+            fprintf(stderr, "Unrecognized option: '%s'\n", argv[argi]);
+            usage(argv[0]);
+        }
+    }
+
+    if (argc < argi + 2) {
+        fprintf(stderr, "Missing parameters\n");
+        usage(argv[0]);
+    }
+
+    f = fopen(argv[argi + 0], "r");
+    if (!f) {
+        perror("fopen");
+        return 1;
+    }
+
+    // Find the "header" in the file
+    if (!offset) {
+        fseek(f, 0, SEEK_END);
+    } else if (offset < 0) {
+        fseek(f, offset, SEEK_END);
+    } else if (offset > 0) {
+        fseek(f, offset, SEEK_SET);
+    }
+
+    // Figure out the length and decompressed length of the file
+    uint32_t f_len;
+    uint32_t f_declen;
+    fseek(f, -(sizeof(f_declen) + sizeof(f_len)), SEEK_CUR);
+    if (fread(&f_len, sizeof(f_len), 1, f) != 1) {
+        perror("fread");
+        return 1;
+    }
+    if (fread(&f_declen, sizeof(f_declen), 1, f) != 1) {
+        perror("fread");
+        return 1;
+    }
+    f_len = f_len & 0xFFFFFF;
+    if (f_len % 4 != 0) f_len += 4 - (f_len % 4);
+    f_declen += f_len;
+    if (fseek(f, -(size_t)f_len, SEEK_CUR)) {
+        perror("fseek");
+        return 1;
+    }
+
+    // Read the file
+    void *file = malloc(f_declen);
+    if (!file) {
+        perror("malloc");
+        return 1;
+    }
+    if (fread(file, 1, f_len, f) != f_len) {
+        perror("fread");
+        return 1;
+    }
+    fclose(f);
+
+    nitro_decompress((char *)file + f_len);
+
+    // Save the output
+    f = fopen(argv[argi + 1], "w");
+    if (!f) {
+        perror("fopen");
+        return 1;
+    }
+    fwrite(file, f_declen, 1, f);
+    fclose(f);
+    free(file);
+
+    return 0;
+}