From 8b38afbb7f79821686cb7f5c96fae29ef146ca62 Mon Sep 17 00:00:00 2001
From: Connor Olding <cloningdonor@gmail.com>
Date: Wed, 20 Jul 2016 19:21:33 -0700
Subject: [PATCH] add a dedicated crc tool for convenience

---
 z64crc.c | 210 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 210 insertions(+)
 create mode 100644 z64crc.c

diff --git a/z64crc.c b/z64crc.c
new file mode 100644
index 0000000..a0375a2
--- /dev/null
+++ b/z64crc.c
@@ -0,0 +1,210 @@
+// Based on uCON64's N64 checksum algorithm by Andreas Sterbenz
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+typedef uint32_t u32;
+typedef uint8_t u8;
+
+static const u32
+CRC_SEEDS[] = {
+    0,
+    0xF8CA4DDC, // 6101
+    0xF8CA4DDC, // 6102
+    0xA3886759, // 6103
+    0,
+    0xDF26F436, // 6105
+    0x1FEA617A  // 6106
+};
+
+const static u32
+BOOTCODE_CRCS[] = {
+    0,
+    0x6170A4A1, // 6101
+    0x90BB6CB5, // 6102
+    0x0B050EE0, // 6103
+    0,
+    0x98BC2C86, // 6105
+    0xACC8580A  // 6106
+};
+
+#define N_CRC (sizeof(CRC_SEEDS) / sizeof(CRC_SEEDS[0]))
+
+// crc32 code via https://gist.github.com/notwa/5689243
+// in turn via http://www.geocities.ws/malbrain/crc_c.html
+
+static const u32 crc32_tbl[] = {
+    0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC,
+    0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C,
+    0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C,
+    0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
+};
+
+static inline u32
+calc_crc32(u8 *ptr, int cnt, u32 crc) {
+    while (cnt--) {
+        crc = (crc >> 4) ^ crc32_tbl[(crc & 0xF) ^ (*ptr & 0xF)];
+        crc = (crc >> 4) ^ crc32_tbl[(crc & 0xF) ^ (*(ptr++) >> 4)];
+    }
+    return crc;
+}
+
+static inline u32
+ROL(u32 i, u32 b) {
+    return (i << b) | (i >> (32 - b));
+}
+
+static inline u32
+R4(u8 *b) {
+    return 0x1000000 * b[0] + 0x10000 * b[1] + 0x100 * b[2] + b[3];
+}
+
+static inline u8*
+W4(u8 *b, u32 x) {
+    b[0] = (x >> 24) & 0xFF;
+    b[1] = (x >> 16) & 0xFF;
+    b[2] = (x >>  8) & 0xFF;
+    b[3] = (x >>  0) & 0xFF;
+    return b;
+}
+
+typedef struct {
+    u32 crc1;
+    u32 crc2;
+} calc_crc_ret;
+
+static inline calc_crc_ret
+calc_crc(u8 *data, int bootcode, u8 *lookup) {
+    calc_crc_ret ret = {};
+
+    u32 seed = CRC_SEEDS[bootcode];
+    u32 t1 = seed;
+    u32 t2 = seed;
+    u32 t3 = seed;
+    u32 t4 = seed;
+    u32 t5 = seed;
+    u32 t6 = seed;
+
+    for (size_t i = 0x1000; i < 0x101000; i += 4) {
+        u32 d = R4(data + i);
+
+        if (t6 + d < t6)
+            t4++;
+
+        t6 += d;
+
+        t3 ^= d;
+
+        u32 r = ROL(d, d & 0x1F);
+
+        t5 += r;
+
+        if (t2 > d)
+            t2 ^= r;
+        else
+            t2 ^= t6 ^ d;
+
+        if (bootcode == 5) {
+            u32 o = i & 0xFF;
+            t1 += R4(lookup + o) ^ d;
+        } else {
+            t1 += t5;
+        }
+    }
+
+    if (bootcode == 3) {
+        ret.crc1 = (t6 ^ t4) + t3;
+        ret.crc2 = (t5 ^ t2) + t1;
+    } else if (bootcode == 6) {
+        ret.crc1 = t6 * t4 + t3;
+        ret.crc2 = t5 * t2 + t1;
+    } else {
+        ret.crc1 = t6 ^ t4 ^ t3;
+        ret.crc2 = t5 ^ t2 ^ t1;
+    }
+
+    return ret;
+}
+
+static int
+crc_version(u8 *buf) {
+    // returns negative on error
+    // otherwise returns version index
+    u32 bootsum = ~calc_crc32(buf + 0x40, 0x1000 - 0x40, ~0);
+
+    if (bootsum == 0)
+        return -1;
+
+    for (int i = 0; i < N_CRC; i++)
+        if (bootsum == BOOTCODE_CRCS[i])
+            return i;
+
+    return -1;
+}
+
+static int
+fix_crc(u8 *buf) {
+    // returns negative on error
+    // otherwise returns version index
+    // and modifies the buffer
+    int bootcode = crc_version(buf);
+    if (bootcode < 0)
+        return bootcode;
+
+    calc_crc_ret crcs = calc_crc(buf, bootcode, buf + 0x750);
+    W4(buf + 0x10, crcs.crc1);
+    W4(buf + 0x14, crcs.crc2);
+
+    return bootcode;
+}
+
+int
+main(int argc, char *argv[]) {
+    // TODO: add stdin/stdout mode
+    for (int i = 1; i < argc; i++) {
+        FILE *f = fopen(argv[i], "rb");
+        if (f == NULL) {
+            perror(argv[1]);
+            return 1;
+        }
+
+        fseek(f, 0, SEEK_END);
+        size_t size = ftell(f);
+        fseek(f, 0, SEEK_SET);
+
+        if (size < 0x00101000 || size > 0x10000000) {
+            fprintf(stderr, "Expected reasonable ROM size, got 0x%08X\n", (u32) size);
+            fclose(f);
+            return 2;
+        }
+
+        u8 *buf = malloc(size);
+        fread(buf, 1, size, f);
+        fclose(f);
+
+        int bootcode = fix_crc(buf);
+        if (bootcode < 0) {
+            //fprintf(stderr, "Failed to fix CRC. Error %i\n", bootcode);
+            fprintf(stderr, "Failed to fix CRC: unknown bootcode\n");
+            free(buf);
+            return bootcode;
+        }
+
+        f = fopen(argv[i], "wb");
+        if (f == NULL) {
+            perror(argv[1]);
+            return 3;
+        }
+
+        fwrite(buf, size, 1, f);
+        fclose(f);
+
+        printf("%i\t%s\n", bootcode + 6100, argv[i]);
+
+        free(buf);
+    }
+
+    return 0;
+}