如果lua数是双数，=/< =/>操作是否总是正确? [英] if lua number is double, does =/<=/>= operations always correct?

问题描述

如您所知，浮点数存在精度问题，即值1将为0.9999999.lua在C中使用==来检查两个双数是否相等.所以问题是:

As you know, float point has a precision problem, that is a value 1 will be 0.9999999. And lua use == in C to check whether two double numbers equal. So the problem is:

a = 5.6
b = 14 * 0.4
print(a==b) ; => false

但更糟糕的是:

a = 1
...
if a < 1 then print("<1") end ; => sometimes a < 1 

那么我该如何避免呢?我签出了lua源代码，看来我可以在luaconf.h中修改luai_numeq/luai_numle)宏，但这是必需的吗?

So how can i avoid this ? I check out lua source code, it seems i can modify luai_numeq/luai_numle) macros in luaconf.h, but is this necessary ?

更新

第二个例子并不正确.实际上，我的问题是，我将值1传递给使用lua_tonumber来获取值的c/c ++，并将此值存储在double变量中，并在一段时间后将值(lua_pushnumber)推入lua，并且将<1发生了:

The second example is not really correct. Actually my problem is, I pass a value 1 to c/c++ which use lua_tonumber to get the value, and i store this value in a double variable, and after sometime, I push the value (lua_pushnumber) to lua, and a < 1 happened:

in lua:
my_cfunction(1)
...
in c:
int my_cfunction(lua_State *L) {
    double val = lua_tonumber(L, 1);
    ...
...
lua_pushnumber(L, val);

in lua:
local a = my_cfunction2()
if a < 1 then ... end

推荐答案

浮点数存在精度问题

float point has a precision problem

没有.

与32位整数相比，64位double可以容纳更多的整数值.

A 64 bit double can hold many more integer values precisely than a 32 bit integer.

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