Add RANDOMIZE command

We use our own RNG instead of the C library RNG; this should ensure that
demo.6502 builds an identical demo.ssd on all platforms.

Thanks to "sweh" for pointing out a bug (now fixed) in beebasm_rand()
during development.

Author: ZornsLemma

about.txt

@@ -657,6 +657,13 @@ ASSERT a [, b, c, ...]
   Abort assembly if any of the expressions is false.
 
 
+RANDOMIZE <n>
+
+  Seed the random number generator used by the RND() function.  If this is
+  not used, the random number generator is seeded based on the current time
+  and so each build of a program using RND() will be different.
+
+
 
 
 7. TIPS AND TRICKS
@@ -763,6 +770,7 @@ based on the above demo, but it runs at a low address (&300).
 
 9. VERSION HISTORY
 
+23/04/2016        Added RANDOMIZE
 12/03/2016	  Improved error handling in PUTFILE/PUTBASIC
 		  Added optional automatic line numbering for PUTBASIC
                   Added ASSERT

demo.6502

@@ -50,6 +50,11 @@ ORG 0
 .behindflag		SKIP 1
 
 
+\\ Seed the random number generator so the build is repeatable
+
+RANDOMIZE 42
+
+
 \\ Set start address
 
 ORG &1100

demo.ssd

@@ -35,6 +35,7 @@
 #include "asmexception.h"
 #include "discimage.h"
 #include "BASIC.h"
+#include "random.h"
 
 
 using namespace std;
@@ -75,7 +76,8 @@ const LineParser::Token	LineParser::m_gaTokenTable[] =
 	{ "MACRO",		&LineParser::HandleMacro,				&SourceFile::StartMacro },
 	{ "ENDMACRO",	&LineParser::HandleEndMacro,			&SourceFile::EndMacro },
 	{ "ERROR",		&LineParser::HandleError,				0 },
-	{ "COPYBLOCK",	&LineParser::HandleCopyBlock,			0 }
+	{ "COPYBLOCK",	&LineParser::HandleCopyBlock,			0 },
+	{ "RANDOMIZE",  &LineParser::HandleRandomize,			0 }
 };
 
 
@@ -1986,3 +1988,38 @@ void LineParser::HandleCopyBlock()
 		throw AsmException_SyntaxError_UnexpectedComma( m_line, m_column );
 	}
 }
+
+
+/*************************************************************************************************/
+/**
+	LineParser::HandleRandomize()
+*/
+/*************************************************************************************************/
+void LineParser::HandleRandomize()
+{
+	unsigned int value;
+
+	try
+	{
+		value = EvaluateExpressionAsUnsignedInt();
+	}
+	catch ( AsmException_SyntaxError_SymbolNotDefined& )
+	{
+		if ( GlobalData::Instance().IsFirstPass() )
+		{
+			value = 0;
+		}
+		else
+		{
+			throw;
+		}
+	}
+
+	beebasm_srand( value );
+
+	if ( m_column < m_line.length() && m_line[ m_column ] == ',' )
+	{
+		// Unexpected comma (remembering that an expression can validly end with a comma)
+		throw AsmException_SyntaxError_UnexpectedComma( m_line, m_column );
+	}
+}

src/commands.cpp

@@ -35,6 +35,7 @@
 #include "globaldata.h"
 #include "objectcode.h"
 #include "sourcefile.h"
+#include "random.h"
 
 
 using namespace std;
@@ -1306,11 +1307,11 @@ void LineParser::EvalRnd()
 	}
 	else if ( val == 1.0f )
 	{
-		result = rand() / ( static_cast< double >( RAND_MAX ) + 1.0 );
+		result = beebasm_rand() / ( static_cast< double >( BEEBASM_RAND_MAX ) + 1.0 );
 	}
 	else
 	{
-		result = static_cast< double >( static_cast< int >( rand() / ( static_cast< double >( RAND_MAX ) + 1.0 ) * val ) );
+		result = static_cast< double >( static_cast< int >( beebasm_rand() / ( static_cast< double >( BEEBASM_RAND_MAX ) + 1.0 ) * val ) );
 	}
 
 	m_valueStack[ m_valueStackPtr - 1 ] = result;

src/expression.cpp

@@ -74,7 +74,6 @@ class GlobalData
 	bool						m_bUseDiscImage;
 	DiscImage*					m_pDiscImage;
 	int							m_forId;
-	int							m_randomSeed;
 	bool						m_bSaved;
 	const char*					m_pOutputFile;
 	int							m_numAnonSaves;

src/globaldata.h

@@ -156,6 +156,7 @@ class LineParser
 	void			HandleEndMacro();
 	void			HandleError();
 	void			HandleCopyBlock();
+	void			HandleRandomize();
 
 	// expression evaluating methods
 

src/lineparser.h

@@ -36,6 +36,7 @@
 #include "discimage.h"
 #include "BASIC.h"
 #include "macro.h"
+#include "random.h"
 
 
 using namespace std;
@@ -235,7 +236,7 @@ int main( int argc, char* argv[] )
 			GlobalData::Instance().SetPass( pass );
 			ObjectCode::Instance().InitialisePass();
 			GlobalData::Instance().ResetForId();
-			srand( static_cast< unsigned int >( randomSeed ) );
+			beebasm_srand( static_cast< unsigned long >( randomSeed ) );
 			SourceFile input( pInputFile );
 			input.Process();
 		}

src/main.cpp

@@ -0,0 +1,49 @@
+/*************************************************************************************************/
+/**
+	random.cpp
+
+        Simple Lehmer random number generator; used instead of the native C library's generator 
+        so RANDOMIZE+RND() gives consistent results on all platforms. The constants used are those
+        for C++11's minstd_rand. See https://en.wikipedia.org/wiki/Lehmer_random_number_generator
+
+	Copyright (C) Rich Talbot-Watkins 2007 - 2012
+	Copyright (C) Steven Flintham 2016
+
+	This file is part of BeebAsm.
+
+	BeebAsm 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.
+
+	BeebAsm 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 BeebAsm, as
+	COPYING.txt.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/*************************************************************************************************/
+
+#include "random.h"
+
+static unsigned long state = 19670512;
+
+static unsigned long modulus = BEEBASM_RAND_MODULUS;
+
+void beebasm_srand(unsigned long seed)
+{
+        state = seed % modulus;
+        if ( state == 0 )
+        {
+                state = 1;
+        }
+}
+
+unsigned long beebasm_rand()
+{
+        state = ( BEEBASM_RAND_MULTIPLIER * state ) % modulus;
+        // It's always true that 1 <= state <= (modulus - 1), so we return state - 1 to make
+        // 0 a possible value. BEEBASM_RAND_MAX is modulus - 2, so we have 0 <= return value <=
+        // BEEBASM_RAND_MAX as required for compatibility with the interface of rand().
+        return state - 1;
+}

src/random.cpp

@@ -0,0 +1,35 @@
+/*************************************************************************************************/
+/**
+	random.h
+
+
+	Copyright (C) Rich Talbot-Watkins 2007 - 2012
+	Copyright (C) Steven Flintham 2016
+
+	This file is part of BeebAsm.
+
+	BeebAsm 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.
+
+	BeebAsm 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 BeebAsm, as
+	COPYING.txt.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/*************************************************************************************************/
+
+#ifndef RANDOM_H_
+#define RANDOM_H_
+
+#define BEEBASM_RAND_MULTIPLIER (48271UL)
+#define BEEBASM_RAND_MODULUS (2147483647UL)
+#define BEEBASM_RAND_MAX (BEEBASM_RAND_MODULUS - 2UL)
+
+void beebasm_srand(unsigned long seed);
+
+unsigned long beebasm_rand();
+
+#endif // RANDOM_H_