forth - GForth:将 float 转换为字符串

Question

一个简单的问题，结果证明是相当复杂的:

如何在 GForth 中将浮点数转换为字符串？所需的行为看起来像这样:

1.2345e fToString \ takes 1.2345e from the float stack and pushes (addr n) onto the data stack

Answer 1

经过一番挖掘，我的一位同事发现了它:

f>str-rdp ( rf +nr +nd +np -- c-addr nr )

https://www.complang.tuwien.ac.at/forth/gforth/Docs-html-history/0.6.2/Formatted-numeric-output.html

Convert rf into a string at c-addr nr. The conversion rules and the meanings of nr +nd np are the same as for f.rdp.

来自 f.rdp :

f.rdp ( rf +nr +nd +np – )

https://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Simple-numeric-output.html

Print float rf formatted. The total width of the output is nr. For fixed-point notation, the number of digits after the decimal point is +nd and the minimum number of significant digits is np. Set-precision has no effect on f.rdp. Fixed-point notation is used if the number of siginicant digits would be at least np and if the number of digits before the decimal point would fit. If fixed-point notation is not used, exponential notation is used, and if that does not fit, asterisks are printed. We recommend using nr>=7 to avoid the risk of numbers not fitting at all. We recommend nr>=np+5 to avoid cases where f.rdp switches to exponential notation because fixed-point notation would have too few significant digits, yet exponential notation offers fewer significant digits. We recommend nr>=nd+2, if you want to have fixed-point notation for some numbers. We recommend np>nr, if you want to have exponential notation for all numbers.

用人类可读的术语来说，这些函数需要浮点堆栈上的一个数字和数据堆栈上的三个数字。

第一个数字参数告诉它字符串应该有多长，第二个告诉它你想要多少小数，第三个告诉它最小的小数位数(大致转换为精度)。执行大量隐式数学运算以确定生成的最终 String 格式，因此几乎需要进行一些修补才能使其按照您想要的方式运行。

测试一下(我们不想重建 f. ，而是要生成一种格式，该格式将被再次接受为 EVALUATE 的浮点数，因此 1.2345E0 表示法是故意的):

PI 18 17 17 f>str-rdp type \ 3.14159265358979E0 ok
PI 18 17 17 f.rdp          \ 3.14159265358979E0 ok
PI f.                      \ 3.14159265358979  ok