GLK: ALAN3: Initial files commit

1 files changed, 182 insertions, 0 deletions

diff --git a/engines/glk/alan3/decode.cpp b/engines/glk/alan3/decode.cpp
new file mode 100644
index 0000000000..c06d19aa48
--- /dev/null
+++ b/engines/glk/alan3/decode.cpp
@@ -0,0 +1,182 @@
+/* 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 2
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+#include "glk/alan3/decode.h"
+#include "glk/alan3/acode.h"
+#include "glk/alan3/syserr.h"
+#include "glk/alan3/exe.h"
+#include "glk/alan3/memory.h"
+
+namespace Glk {
+namespace Alan3 {
+
+/* PUBLIC DATA */
+Aword *freq;            /* Cumulative character frequencies */
+
+
+/* PRIVATE DATA */
+/* Bit output */
+static int decodeBuffer;	/* Bits to be input */
+static int bitsToGo;		/* Bits still in buffer */
+static int garbageBits;		/* Bits past EOF */
+
+
+static int inputBit(void)
+{
+  int bit;
+
+  /* More bits available ? */
+  if (!bitsToGo) {
+	/* No, so get more */
+	 decodeBuffer = (textFile->pos() >= textFile->size()) ? EOF : textFile->readByte();
+    if (decodeBuffer == EOF) {
+      garbageBits++;
+      if (garbageBits > VALUEBITS-2)
+	syserr("Error in encoded data file.");
+    } else
+      bitsToGo = 8;		/* Another Char, 8 new bits */
+  }
+  bit = decodeBuffer&1;		/* Get next bit */
+  decodeBuffer = decodeBuffer>>1; /* and remove it */
+  bitsToGo--;
+  return bit;
+}
+
+
+/* Current state of decoding */
+
+static CodeValue value;			/* Currently seen code value */
+static CodeValue low, high;		/* Current code region */
+
+
+void startDecoding(void)
+{
+  int i;
+
+  bitsToGo = 0;
+  garbageBits = 0;
+
+  value = 0;
+  for (i = 0; i < VALUEBITS; i++)
+    value = 2*value + inputBit();
+  low = 0;
+  high = TOPVALUE;
+}
+
+
+int decodeChar(void)
+{
+  long range;
+  int f;
+  int symbol;
+
+  range = (long)(high-low) + 1;
+  f = (((long)(value-low)+1)*freq[0]-1)/range;
+
+  /* Find the symbol */
+  for (symbol = 1; freq[symbol] > f; symbol++);
+
+  high = low + range*freq[symbol-1]/freq[0]-1;
+  low = low + range*freq[symbol]/freq[0];
+
+  for (;;) {
+    if (high < HALF)
+      ;
+    else if (low >= HALF) {
+      value = value - HALF;
+      low = low - HALF;
+      high = high - HALF;
+    } else if (low >= ONEQUARTER && high < THREEQUARTER) {
+      value = value - ONEQUARTER;
+      low = low - ONEQUARTER;
+      high = high - ONEQUARTER;
+    } else
+      break;
+
+    /* Scale up the range */
+    low = 2*low;
+    high = 2*high+1;
+    value = 2*value + inputBit();
+  }
+  return symbol-1;
+}
+
+
+
+/* Structure for saved decode info */
+struct DecodeInfo {
+  long fpos;
+  int buffer;
+  int bits;
+  CodeValue value;
+  CodeValue high;
+  CodeValue low;
+};
+
+
+/*======================================================================
+
+  pushDecode()
+
+  Save so much info about the decoding process so it is possible to
+  restore and continue later.
+
+ */
+void *pushDecode(void)
+{
+  DecodeInfo *info;
+
+  info = (DecodeInfo *)allocate(sizeof(DecodeInfo));
+  info->fpos = textFile->pos();
+  info->buffer = decodeBuffer;
+  info->bits = bitsToGo;
+  info->value = value;
+  info->high = high;
+  info->low = low;
+  return(info);
+}
+
+
+/*======================================================================
+
+  popDecode()
+
+  Restore enough info about the decoding process so it is possible to
+  continue after having decoded something else.
+
+ */
+void popDecode(void *i)
+{
+  DecodeInfo *info = (DecodeInfo *) i;
+
+  textFile->seek(info->fpos);
+  decodeBuffer = info->buffer;
+  bitsToGo = info->bits;
+  value = info->value;
+  high = info->high;
+  low = info->low;
+
+  free(info);
+}
+
+} // End of namespace Alan3
+} // End of namespace Glk