added: static sint UInt<value_size>::FindLowestBitInWord(uint x)

(asm_vc_32, asm_gcc_32, no_asm, and intrinsic for vc64)



git-svn-id: svn://ttmath.org/publicrep/ttmath/trunk@275 e52654a7-88a9-db11-a3e9-0013d4bc506e

CHANGELOG

@@ -34,8 +34,10 @@ Version 0.9.1 prerelease (2009.12.28):
                - and the exponent is smaller than about 2 times the number of bits from the mantissa
                this helps to correctly calculate expressions such as: "0.80-3*0.34+0.22"
                now the parser gives zero (previous there was a value very closed to zero)
+    * added:   static sint UInt<value_size>::FindLowestBitInWord(uint x)
+               this method is looking for the lowest set bit in a word
     * added:   UInt::FindLowestBit(uint & table_id, uint & index)
-               /temporarily version - asm version is missing /
+               this method is looking for the lowest set bit
 
                
 Version 0.9.0 (2009.11.25):

ttmath/ttmathuint.h

@@ -672,27 +672,14 @@ public:
 		if( table_id >= value_size )
 		{
 			// is zero
-			index = 0;
+			index    = 0;
 			table_id = 0;
 
 		return false;
 		}
 		
 		// table[table_id] is different from 0
-
-		// !! need asm version:
-		// index = FindSmallestBitInWord( table[table_id] );
-
-		index = 0;
-		uint temp = table[table_id];
-
-		while( (temp & 1) == 0 )
-		{
-			index += 1;
-			temp >>= 1;
-		}
-
-		// !!
+		index = FindLowestBitInWord( table[table_id] );
 
 	return true;
 	}
@@ -3498,6 +3485,7 @@ public:
 	uint SubInt(uint value, uint index = 0);
 	static uint SubVector(const uint * ss1, const uint * ss2, uint ss1_size, uint ss2_size, uint * result);
 	static sint FindLeadingBitInWord(uint x);
+	static sint FindLowestBitInWord(uint x);
 	static uint SetBitInWord(uint & value, uint bit);
 	static void MulTwoWords(uint a, uint b, uint * result_high, uint * result_low);
 	static void DivTwoWords(uint a,uint b, uint c, uint * r, uint * rest);

ttmath/ttmathuint_noasm.h

@@ -588,6 +588,27 @@ namespace ttmath
 
 
 
+	/*!
+		this method returns the number of the highest set bit in x
+		if the 'x' is zero this method returns '-1'
+	*/
+	template<uint value_size>
+	sint UInt<value_size>::FindLowestBitInWord(uint x)
+	{
+		if( x == 0 )
+			return -1;
+
+		uint bit = 0;
+		
+		while( (x & 1) == 0 )
+		{
+			x = x >> 1;
+			++bit;
+		}
+
+	return bit;
+	}
+
 
 
 	/*!

ttmath/ttmathuint_x86.h

@@ -1353,6 +1353,50 @@ namespace ttmath
 
 
 
+	/*
+		this method returns the number of the smallest set bit in one 32-bit word
+		if the 'x' is zero this method returns '-1'
+	*/
+	template<uint value_size>
+	sint UInt<value_size>::FindLowestBitInWord(uint x)
+	{
+	sint result;
+
+		#ifndef __GNUC__
+			__asm
+			{
+				push eax
+				push edx
+
+				mov edx,-1
+				bsf eax,[x]
+				cmovz eax,edx
+				mov [result], eax
+
+				pop edx
+				pop eax
+			}
+		#endif
+
+
+		#ifdef __GNUC__
+		uint dummy;
+
+				__asm__ (
+
+				"movl $-1, %1          \n"
+				"bsfl %2, %0           \n"
+				"cmovz %1, %0          \n"
+
+				: "=r" (result), "=&r" (dummy)
+				: "r" (x)
+				: "cc" );
+
+		#endif
+
+	return result;
+	}
+
 
 
 	/*!

ttmath/ttmathuint_x86_64.h

@@ -987,6 +987,55 @@ namespace ttmath
 	}
 
 
+	/*
+		this method returns the number of the highest set bit in one 64-bit word
+		if the 'x' is zero this method returns '-1'
+
+		***this method is created only on a 64bit platform***
+	*/
+	template<uint value_size>
+	sint UInt<value_size>::FindLowestBitInWord(uint x)
+	{
+	sint result;
+
+
+		#if !defined(__GNUC__) && !defined(_MSC_VER)
+			#error "another compiler than GCC or Microsoft VC is currently not supported in 64bit mode, you can compile with TTMATH_NOASM macro"
+		#endif
+
+		
+		#ifdef _MSC_VER
+
+			unsigned long nIndex = 0;
+
+			if( _BitScanForward64(&nIndex,x) == 0 )
+				result = -1;
+			else
+				result = nIndex;
+
+		#endif
+
+
+		#ifdef __GNUC__
+		uint dummy;
+
+				__asm__ (
+
+				"movq $-1, %1          \n"
+				"bsfq %2, %0           \n"
+				"cmovz %1, %0          \n"
+
+				: "=r" (result), "=&r" (dummy)
+				: "r" (x)
+				: "cc" );
+
+		#endif
+
+
+	return result;
+	}
+
+
 	/*!
 		this method sets a special bit in the 'value'
 		and returns the last state of the bit (zero or one)