gnuplot对浮点数的内部表示是什么? [英] What is gnuplot's internal representation of floating point numbers?

问题描述

我确定答案是显而易见的，但是如果不查看源代码，我将找不到答案.

I'm sure the answer is obvious but I can't find it without looking at the source.

gnuplot对浮点数的内部表示是什么?是平台的double吗?它是否使用自己的内部表示形式?可以做到任意精度吗?

What is gnuplot's internal representation of floating point numbers? Is it the platform's double? Does it use its own internal representation? Can it do arbitrary precision?

推荐答案

通过Google进行快速搜索，发现只要有可能，计算就会以双精度进行，但是，这里有一些小功能. IEEE双精度数字的范围应该大于1.797e308，但是，如果您尝试给gnuplot一个如此大的数字，则会令人窒息:

A quick google search will turn up that calculations are done in double precision whenever possible, however, there's a little sublety going on here. The range of an IEEE double precision number should go up to more than 1.797e308, however, if you try to give gnuplot a number that big, it chokes:

gnuplot> plot '-' u 0:($1/2.)
input data ('e' ends) > 1.7976931348623157e+308
input data ('e' ends) > 30
input data ('e' ends) > e
Warning: empty x range [1:1], adjusting to [0.99:1.01]
Warning: empty y range [15:15], adjusting to [14.85:15.15]

现在，如果您显示gnuplot的范围变量:

Now if you show gnuplot's range variables:

gnuplot> show variables all

您会看到一些有点奇怪的东西:

You'll see some things that are a little strange:

GPVAL_DATA_X2_MIN = 8.98846567431158e+307
GPVAL_DATA_X2_MAX = -8.98846567431158e+307

此数字重复几次. (请注意，这个数字大致上是 ):

With this number repeated a few times. (Note that this number is roughly correct):

gnuplot> !python -c 'import sys; print sys.float_info.max/2.'
8.98846567431e+307

**(python的float是系统的双精度).

**(python's float is the system's double precision).

现在玩一点:

gnuplot> a = 8.98846567431e+307
gnuplot> a = 8.98846567432e+307
             ^
         undefined value

因此gnuplot的浮点数可能会达到系统的最大值，以双精度(在可能的情况下)除以2.

So presumably gnuplot's floating point numbers go up to the system's maximum for double precision (where possible) divided by 2.

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