14.7.1 Multiplication operator

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本文详细介绍了在不同上下文中整数、浮点数及十进制数乘法运算符的重载实现，包括其参数类型转换、结果类型确定、溢出处理等方面的内容。

For an operation of the form x * y, binary operator overload resolution (?4.
2.4) is applied to select a
specific operator implementation. The operands are converted to the
parameter types of the selected
operator, and the type of the result is the return type of the operator.
The predefined multiplication operators are listed below. The operators all
compute the product of x and y.
?Integer multiplication:
int operator *(int x, int y);
uint operator *(uint x, uint y);
long operator *(long x, long y);
ulong operator *(ulong x, ulong y);
In a checked context, if the product is outside the range of the result
type, a
System.OverflowException is thrown. In an unchecked context, overflows are
not reported and
any significant high-order bits outside the range of the result type are
discarded.
?Floating-point multiplication:
float operator *(float x, float y);
double operator *(double x, double y);
Chapter 14 Expressions
157
The product is computed according to the rules of IEC 60559 arithmetic. The
following table lists the
results of all possible combinations of nonzero finite values, zeros,
infinities, and NaN?s. In the table, x
and y are positive finite values. z is the result of x * y. If the result
is too large for the destination type,
z is infinity. If the result is too small for the destination type, z is
zero.

      +y    -y    +0    -0    +8    -8    NaN
+x    +z    -z    +0    -0    +8    -8    NaN
-x    -z    +z    -0    +0    -8    +8    NaN
+0    +0    -0    +0    -0    NaN   NaN   NaN
-0    -0    +0    -0    +0    NaN   NaN   NaN
+8    +8    -8    NaN   NaN   +8    -8    NaN
-8    -8    +8    NaN   NaN   -8    +8    NaN
NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN

?Decimal multiplication:
decimal operator *(decimal x, decimal y);
If the resulting value is too large to represent in the decimal format, a
System.OverflowException
is thrown. If the result value is too small to represent in the decimal
format, the result is zero. The scale
of the result, before any rounding, is the sum of the scales of the two
operands.
Decimal multiplication is equivalent to using the multiplication operator
of type System.Decimal.