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engines/glk/scott/decompress_text.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/*
+ * Based on ScottFree interpreter version 1.14 developed by Swansea
+ * University Computer Society without disassembly of any other game
+ * drivers, only of game databases as permitted by EEC law (for purposes
+ * of compatibility).
+ *
+ * Licensed under GPLv2
+ *
+ * https://github.com/angstsmurf/spatterlight/tree/master/terps/scott
+ */
+
+#include "common/str.h"
+#include "glk/scott/decompress_text.h"
+
+namespace Glk {
+namespace Scott {
+
+int rotateLeftWithCarry(uint8_t *byte, int lastCarry) {
+	int carry = ((*byte & 0x80) > 0);
+	*byte = *byte << 1;
+	if (lastCarry)
+		*byte = *byte | 0x01;
+	return carry;
+}
+
+int decompressOne(uint8_t *bytes) {
+	uint8_t result = 0;
+	int carry;
+	for (int i = 0; i < 5; i++) {
+		carry = 0;
+		for (int j = 0; j < 5; j++) {
+			carry = rotateLeftWithCarry(bytes + 4 - j, carry);
+		}
+		rotateLeftWithCarry(&result, carry);
+	}
+	return result;
+}
+
+char *decompressText(uint8_t *source, int stringIndex) {
+	// Lookup table
+	const char *alphabet = " abcdefghijklmnopqrstuvwxyz'\x01,.\x00";
+	//Common::String alphabet = " abcdefghijklmnopqrstuvwxyz'\x01,.\x00";
+
+	int pos, c, uppercase, i, j;
+	uint8_t decompressed[256];
+	uint8_t buffer[5];
+	int idx = 0;
+
+	// Find the start of the compressed message
+	for (i = 0; i < stringIndex; i++) {
+		pos = *source;
+		pos = pos & 0x7F;
+		source += pos;
+	};
+
+	uppercase = ((*source & 0x40) == 0); // Test bit 6
+
+	source++;
+	do {
+		// Get five compressed bytes
+		for (i = 0; i < 5; i++) {
+			buffer[i] = *source++;
+		}
+		for (j = 0; j < 8; j++) {
+			// Decompress one character:
+			int next = decompressOne(buffer);
+
+			c = alphabet[next];
+
+			if (c == 0x01) {
+				uppercase = 1;
+				c = ' ';
+			}
+
+			if (c >= 'a' && uppercase) {
+				c = toupper(c);
+				uppercase = 0;
+			}
+			decompressed[idx++] = c;
+
+			if (idx > 255)
+				return nullptr;
+
+			if (idx == 255)
+				c = 0; // We've gone too far, return
+
+			if (c == 0) {
+				char *result = new char[idx];
+				memcpy(result, decompressed, idx);
+				return result;
+			} else if (c == '.' || c == ',') {
+				if (c == '.')
+					uppercase = 1;
+				decompressed[idx++] = ' ';
+			}
+		}
+	} while (idx < 0xff); // Chosen arbitrarily, might be too small
+	return nullptr;
+}
+
+} // End of namespace Scott
+} // End of namespace Glk