GLK: ARCHETYPE: Fixes for string decryption

3 files changed, 55 insertions, 20 deletions

diff --git a/engines/glk/archetype/crypt.cpp b/engines/glk/archetype/crypt.cpp
index d99dab0907..1b59163daf 100644
--- a/engines/glk/archetype/crypt.cpp
+++ b/engines/glk/archetype/crypt.cpp
@@ -28,10 +28,40 @@ namespace Archetype {
 
 byte CryptMask;
 EncryptionType Encryption;
+static uint RandSeed;
+const int RANDOM_KEY = 33797;
 
 void crypt_init() {
 	Encryption = NONE;
 	CryptMask = 0x55;
+	RandSeed = 0;
+}
+
+static void setDecryptionSeed(uint new_seed) {
+	RandSeed = new_seed;
+}
+
+static void cycleRandomSeed() {
+	uint16 c = RandSeed & 0xffff;
+	uint val = (uint)c * RANDOM_KEY;
+	c <<= 3;
+	c = (c & 0xff) | ((((c >> 8) + c) & 0xff) << 8);
+	val += (uint)c << 16;
+
+	uint16 b = RandSeed >> 16;
+	val += (uint)b << 16;
+	b <<= 2;
+	val += (uint)b << 16;
+	val += (uint)(b & 0xff) << 24;
+	b <<= 5;
+	val += (uint)(b & 0xff) << 24;
+
+	RandSeed = val + 1;
+}
+
+static uint getDeterministicRandomNumber(uint limit) {
+	cycleRandomSeed();
+	return (limit == 0) ? 0 : (RandSeed >> 16) % limit;
 }
 
 void cryptinit(EncryptionType crypt_kind, uint seed) {
@@ -39,37 +69,38 @@ void cryptinit(EncryptionType crypt_kind, uint seed) {
 	Encryption = crypt_kind;
 
 	if (Encryption == COMPLEX)
-		g_vm->setRandomNumberSeed(seed);
+		setDecryptionSeed(seed);
 }
 
-void cryptstr(Common::String &s) {
+void cryptstr(char *buffer, size_t length) {
 	byte nextMask;
+	char *p = buffer;
 
 	switch (Encryption) {
 	case SIMPLE:
-		for (uint i = 0; i < s.size(); ++i)
-			s.setChar(s[i] ^ CryptMask, i);
+		for (size_t i = 0; i < length; ++i, ++p)
+			*p ^= CryptMask;
 		break;
 
 	case PURPLE:
-		for (uint i = 0; i < s.size(); ++i) {
-			s.setChar(s[i] ^ CryptMask, i);
-			CryptMask += s[i] & 7;
+		for (size_t i = 0; i < length; ++i, ++p) {
+			*p ^= CryptMask;
+			CryptMask += *p & 7;
 		}
 		break;
 
 	case UNPURPLE:
-		for (uint i = 0; i < s.size(); ++i) {
-			nextMask = CryptMask + (s[i] & 7);
-			s.setChar(s[i] ^ CryptMask, i);
+		for (size_t i = 0; i < length; ++i, ++p) {
+			nextMask = CryptMask + (*p & 7);
+			*p ^= CryptMask;
 			CryptMask = nextMask;
 		}
 		break;
 
 	case COMPLEX:
-		for (uint i = 0; i < s.size(); ++i) {
-			s.setChar(s[i] ^ CryptMask, i);
-			CryptMask = g_vm->getRandomNumber(0x100);
+		for (size_t i = 0; i < length; ++i, ++p) {
+			*p ^= CryptMask;
+			CryptMask = (byte)getDeterministicRandomNumber(0x100);
 		}
 		break;
 
diff --git a/engines/glk/archetype/crypt.h b/engines/glk/archetype/crypt.h
index d978210e9a..d92fe39cf6 100644
--- a/engines/glk/archetype/crypt.h
+++ b/engines/glk/archetype/crypt.h
@@ -23,8 +23,7 @@
 #ifndef ARCHETYPE_CRYPT
 #define ARCHETYPE_CRYPT
 
-#include "common/scummsys.h"
-#include "common/str.h"
+#include "glk/archetype/string.h"
 
 namespace Glk {
 namespace Archetype {
@@ -56,7 +55,7 @@ extern void cryptinit(EncryptionType crypt_kind, uint seed);
  * if <method> is COMPLEX, a pseudorandom sequence is used to alter the
  * CryptMask.This can make prediction well-nigh impossible.
  */
-extern void cryptstr(Common::String &s);
+extern void cryptstr(char *buffer, size_t length);
 
 } // End of namespace Archetype
 } // End of namespace Glk
diff --git a/engines/glk/archetype/misc.cpp b/engines/glk/archetype/misc.cpp
index e5a858ba00..c10bba1b33 100644
--- a/engines/glk/archetype/misc.cpp
+++ b/engines/glk/archetype/misc.cpp
@@ -155,11 +155,13 @@ String formatFilename(const String &name, const String &ext, bool replace) {
 void load_string(Common::ReadStream *fIn, String &the_string) {
 	char buffer[257];
 	size_t strSize = fIn->readByte();
+	(void)fIn->readByte();		// Redundant second copy of the length
+
 	fIn->read(buffer, strSize);
 	buffer[strSize] = '\0';
 
+	cryptstr(buffer, strSize);
 	the_string = String(buffer);
-	cryptstr(the_string);
 }
 
 void dump_string(Common::WriteStream *fOut, const String &the_string) {
@@ -170,9 +172,12 @@ void dump_string(Common::WriteStream *fOut, const String &the_string) {
 		fOut->write(the_string.c_str(), the_string.size());
 
 	} else {
-		String tmp = the_string;
-		cryptstr(tmp);
-		fOut->write(tmp.c_str(), tmp.size());
+		char buffer[257];
+		strncpy(buffer, the_string.c_str(), 256);
+		buffer[256] = '\0';
+
+		cryptstr(buffer, the_string.size());
+		fOut->write(buffer, the_string.size());
 	}
 }