M4 eval精度 [英] M4 eval precision

问题描述

我试图使用M4宏来生成CSS文件。我愿意输入我的值在px和做简单的数学使用eval（）得到结果在em。不幸的是我没有找到如何获得浮点数。

I'm trying to use M4 macros to generate css files. I'm willing to enter my values in px and do simple math using eval() to get results in em. Unfortunatly I didn't find how to get floats.

define(`FONTSIZE', `13')dnl
define(`LINEHEIGHT', `17')dnl
.content {padding : eval(LINEHEIGHT / FONTSIZE)em}
>>> m4 style.css.m4
>>> .content {padding : 1em}

有任何想法吗？

谢谢！

推荐答案

出于特定目的，表达式可能会变成类似

For your particular purpose the expression may become something like

eval(LINEHEIGHT/FONTSIZE).substr(eval(((LINEHEIGHT%FONTSIZE)*1000)/FONTSIZE + 1000),1)

（当然，使用满足精度要求的10的幂）
这是获取浮动的常见技巧点状结果。其他操作符更复杂，不是说像sin，cos，ln ...这样的函数。

(of course, use the power of 10 that meets your precision requirements) This is a common trick to obtain a floating point-like result from a division. Other operators are more complicated, not to say the functions like sin, cos, ln...

一般来说，原则上可以写一些浮点操作宏用字符串操作和整数运算符实现，但是我认为，当操作不像分区那样简单时，使用由syscmd（）调用的外部程序（bc，gawk ...）更为普遍。

In general it would be possible in principle to write some floating point manipulation macros implemented with string manipulations and integer operators, but I think it's more pratical to use an external program (bc, gawk...) invoked by "syscmd()" when the operations are not as simple as a division.

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