Cleanups, add comments, some fixes.

src/Amount.cpp

@@ -6,12 +6,18 @@
 
 #include "SerializedTypes.h"
 
+// amount = value * [10 ^ offset]
+// representation range is 10^80 - 10^(-80)
+// on the wire, high 8 bits are (offset+142), low 56 bits are value
+// value is zero if amount is zero, otherwise value is 10^15 - (10^16 - 1) inclusive
+
 void STAmount::canonicalize()
 {
 	if(value==0)
 	{
 		offset=0;
 		value=0;
+		return;
 	}
 	while(value<cMinValue)
 	{
@@ -20,7 +26,7 @@ void STAmount::canonicalize()
 		offset-=1;
 	}
 	while(value>cMaxValue)
-	{ // Here we can make it throw on precision loss if we wish: ((value%10)!=0)
+	{
 		if(offset>=cMaxOffset) throw std::runtime_error("value underflow");
 		value/=10;
 		offset+=1;
@@ -32,8 +38,10 @@ void STAmount::canonicalize()
 STAmount* STAmount::construct(SerializerIterator& sit, const char *name)
 {
 	uint64 value = sit.get64();
-	int offset = static_cast<int>(value>>(64-8));
+
-	value&=~(255ull<<(64-8));
+	int offset = static_cast<int>(value >> (64-8));
+	value &= ~(255ull << (64-8));
+
 	if(value==0)
 	{
 		if(offset!=0)
@@ -41,7 +49,7 @@ STAmount* STAmount::construct(SerializerIterator& sit, const char *name)
 	}
 	else
 	{
-		offset-=142;
+		offset -= 142; // center the range
 		if( (value<cMinValue) || (value>cMaxValue) || (offset<cMinOffset) || (offset>cMaxOffset) )
 			throw std::runtime_error("invalid currency value");
 	}
@@ -49,7 +57,7 @@ STAmount* STAmount::construct(SerializerIterator& sit, const char *name)
 }
 
 std::string STAmount::getText() const
-{
+{ // This should be re-implemented to put a '.' in the string form of the integer value
 	std::ostringstream str;
 	str << std::setprecision(16) << static_cast<double>(*this);
 	return str.str();
@@ -57,44 +65,48 @@ std::string STAmount::getText() const
 
 void STAmount::add(Serializer& s) const
 {
-	uint64 v=value;
+	if (value==0)
-	if(v!=0) v+=(static_cast<uint64>(offset+142) << (64-8));
+		s.add64(0);
-	s.add64(v);
+	else
+		s.add64(value + (static_cast<uint64>(offset+142) << (64-8))));
 }
 
 bool STAmount::isEquivalent(const SerializedType& t) const
 {
-	const STAmount* v=dynamic_cast<const STAmount*>(&t);
+	const STAmount* v = dynamic_cast<const STAmount*>(&t);
 	if(!v) return false;
-	return (value==v->value) && (offset==v->offset);
+	return (value == v->value) && (offset == v->offset);
 }
 
 bool STAmount::operator==(const STAmount& a) const
 {
-	return (offset==a.offset) && (value==a.value);
+	return (offset == a.offset) && (value == a.value);
 }
 
 bool STAmount::operator!=(const STAmount& a) const
 {
-	return (offset!=a.offset) || (value!=a.value);
+	return (offset != a.offset) || (value != a.value);
 }
 
 bool STAmount::operator<(const STAmount& a) const
 {
-	if(offset<a.offset) return true;
+	if(value == 0) return false;
-	if(a.offset<offset) return false;
+	if(offset < a.offset) return true;
+	if(a.offset < offset) return false;
 	return value < a.value;
 }
 
 bool STAmount::operator>(const STAmount& a) const
 {
-	if(offset>a.offset) return true;
+	if(value == 0) return a.value != 0;
-	if(a.offset>offset) return false;
+	if(offset > a.offset) return true;
+	if(a.offset > offset) return false;
 	return value > a.value;
 }
 
 bool STAmount::operator<=(const STAmount& a) const
 {
+	if(value == 0) return a.value== 0;
 	if(offset<a.offset) return true;
 	if(a.offset<offset) return false;
 	return value <= a.value;
@@ -102,6 +114,7 @@ bool STAmount::operator<=(const STAmount& a) const
 
 bool STAmount::operator>=(const STAmount& a) const
 {
+	if(value == 0) return true;
 	if(offset>a.offset) return true;
 	if(a.offset>offset) return false;
 	return value >= a.value;
@@ -175,7 +188,7 @@ STAmount operator-(STAmount v1, STAmount v2)
 		v2.value/=10;
 		v2.offset+=1;
 	}
-	if(v1.value < v2.value) throw std::runtime_error("value overflow");
+	if(v1.value < v2.value) throw std::runtime_error("value underflow");
 	return STAmount(v1.name, v1.value - v2.value, v1.offset);
 }
 
@@ -183,22 +196,21 @@ STAmount getRate(const STAmount& offerIn, const STAmount& offerOut)
 {
 	CBigNum numerator, denominator, quotient;
 
-	if(offerOut.value==0) throw std::runtime_error("illegal offer");
+	if(offerOut.value == 0) throw std::runtime_error("illegal offer");
-	if(offerIn.value==0) return STAmount();
+	if(offerIn.value == 0) return STAmount();
 
-	if(	(BN_zero(&numerator)!=1) || (BN_zero(&denominator)!=1) ||
+	// Compute (numerator * 10^16) / denominator
-		(BN_add_word(&numerator, offerIn.value)!=1) ||
+	if(	(BN_zero(&numerator) != 1) || (BN_zero(&denominator) != 1) ||
-		(BN_add_word(&denominator, offerOut.value)!=1) ||
+		(BN_add_word(&numerator, offerIn.value) != 1) ||
-		(BN_mul_word(&numerator, 1000000000000000ull)!=1) ||
+		(BN_add_word(&denominator, offerOut.value) != 1) ||
-		(BN_div(&quotient, NULL, &numerator, &denominator, CAutoBN_CTX())!=1) )
+		(BN_mul_word(&numerator, 10000000000000000ull) != 1) ||
-		throw std::runtime_error("internal bn error");
+		(BN_div(&quotient, NULL, &numerator, &denominator, CAutoBN_CTX()) != 1) )
-
-	int offset=offerIn.offset - offerOut.offset - 15;
-
-	while(BN_num_bits(&quotient)>60)
 	{
-		offset+=3;
+		throw std::runtime_error("internal bn error");
-		BN_div_word(&quotient, 1000);
 	}
-	return STAmount(quotient.getulong(), offset);
+
+	// 10^15 <= quotient <= 10^17
+	assert(BN_num_bytes(&quotient)<=60);
+
+	return STAmount(quotient.getulong(), offerIn.offset - offerOut.offset - 16);
 }