Update zvm with new xorshift generator

curiousdannii · Jul 21, 2016 · f458c45 · f458c45
1 parent 71fc32c
commit f458c45
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Showing 4 changed files with 12 additions and 13 deletions.
diff --git a/lib/parchment-for-inform7.zip b/lib/parchment-for-inform7.zip
diff --git a/lib/zvm.debug.js b/lib/zvm.debug.js
@@ -3,9 +3,9 @@
 ZVM - the ifvms.js Z-Machine (versions 5 and 8)
 ===============================================
 
-Built: 2015-09-06
+Built: 2016-07-21
 
-Copyright (c) 2011-2015 The ifvms.js team
+Copyright (c) 2011-2016 The ifvms.js team
 BSD licenced
 http://github.com/curiousdannii/ifvms.js
 
@@ -1742,7 +1742,7 @@ var VM = Class.subClass({
 Z-Machine runtime functions
 ===========================
 
-Copyright (c) 2015 The ifvms.js team
+Copyright (c) 2016 The ifvms.js team
 BSD licenced
 http://github.com/curiousdannii/ifvms.js
 
@@ -2190,12 +2190,11 @@ TODO:
 		// Based on the discussions in this forum topic, we will not implement the sequential mode recommended in the standard
 		// http://www.intfiction.org/forum/viewtopic.php?f=38&t=16023
 
-		// Instead implement a 16 bit Xorshift generator taken from
-		// http://b2d-f9r.blogspot.com.au/2010/08/16-bit-xorshift-rng.html
-		seed ^= ( seed << 4 ) & 0xFFFF;
-		seed ^= ( seed >> 3 ) & 0xFFFF;
-		this.xorshift_seed = ( seed ^= ( seed << 7 ) & 0xFFFF );
-		return 1 + ( seed % range );
+		// Instead implement a 32 bit Xorshift generator
+		seed ^= ( seed << 13 );
+		seed ^= ( seed >> 17 );
+		this.xorshift_seed = ( seed ^= ( seed << 5 ) );
+		return 1 + ( ( seed & 0x7FFF ) % range );
 	},
 
 	// Request line input