[英]Is floating point multiplication by zero guaranteed to produce zero?
I understand floating point has rounding errors, but I'm wondering if there are certain situations where the error does not apply, such as multiplication by zero . 我知道浮点数有舍入错误,但我想知道是否存在某些错误不适用的情况,例如乘以零。
Does zero times any number = zero for all floating points ? 对于所有浮点,任何数字的零次是否为零?
False: 假:
0f * NAN == NAN
0f * INFINITY == NAN
and ... 和......
0f * -1f == -0f (negative 0f), with 0f == -0f :-)
(on Intel, VC++, and probably on any platform that uses IEEE 754-1985 floating points) (在Intel,VC ++上,可能在任何使用IEEE 754-1985浮点的平台上)
Example on ideone (that uses GCC on some Intel compatible platform probably) 关于ideone的示例(可能在某些Intel兼容平台上使用GCC)
In addition to @xanatos fine answer, consider some of OP's middle-of-the-post concerns: 除了@xanatos的好答案之外, 还要考虑OP的一些中间问题:
I'm wondering if there are certain situations where the (rounding) error does not apply 我想知道是否存在(舍入)错误不适用的某些情况
Candidates include some_double_y = some_double_x * 1.0
and some_double_y = some_double_x + 0.0
may never incur a rounding error. 候选人包括some_double_y = some_double_x * 1.0
和some_double_y = some_double_x + 0.0
可能永远不会产生舍入错误。
Yet even those are suspect due to a compiler may evaluate double
at higher precision considering the FLT_EVAL_METHOD == 2
where "evaluate all operations and constants to the range and precision of the long double
type." 然而,即使是那些也是可疑的,因为编译器可能会以更高的精度评估double
,考虑到FLT_EVAL_METHOD == 2
,其中“评估所有操作和常量到long double
类型的范围和精度”。 In that case, an intermediate some_double_x
may exist as a long double
differing from an apparent double
value of 0.0
or 1.0
. 在这种情况下,中间some_double_x
可以作为与表观double
some_double_x
值0.0
或1.0
不同的long double
some_double_x
存在。
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