某天，小伙伴反馈说程序 panic 在一个比较诡异的地方，差不多是下面的代码。
type Point struct {
X float32
Y float32
}
func Get(p Point) {
// import github.com/shopspring/decimal
x, _ := decimal.NewFromFloat32(p.X).Round(7).Float64()
}
查看 decimal 的源码，下面是其注释，发现若 value 为 NaN 或者 +/- inf 时，会 panic。
// NewFromFloat32 converts a float32 to Decimal.
//
// The converted number will contain the number of significant digits that can be
// represented in a float with reliable roundtrip.
// This is typically 6-8 digits depending on the input.
// See https://www.exploringbinary.com/decimal-precision-of-binary-floating-point-numbers/ for more information.
//
// For slightly faster conversion, use NewFromFloatWithExponent where you can specify the precision in absolute terms.
//
// NOTE: this will panic on NaN, +/-inf
func NewFromFloat32(value float32) Decimal {
if value == 0 {
return New(0, 0)
}
// XOR is workaround for https://github.com/golang/go/issues/26285
a := math.Float32bits(value) ^ 0x80808080
return newFromFloat(float64(value), uint64(a)^0x80808080, &float32info)
}
显然我们不可能传递一个非法的 p，在我们的认知里面，X 不应该有 NaN 这种数值，即使 p 没有初始化，那也应该不是 NaN。
最终分析的结果是，X 有一个赋值操作，出现 p.X = number / float32(a) ，而 a 有可能是 0，因为在我的认知里面，除法除 0 就会 panic，而不可能到调用 NewFromFloat32 时才出问题，最后发现一个惊人的事实：只有整数除 0 才会 panic，除以 0.0 并不会引发 panic，而会得到 NaN/+Inf/-Inf。
这让我突然有想研究各个语言在在除 0 以及 0.0 的想法了。
关于浮点数除 0 为什么不会报错，此处是相关的链接。
Rust
浮点数相除的结果是注释掉编译错误之后得到的结果。
rustc 1.55.0 (c8dfcfe04 2021-09-06)
fn main() {
let a = 0;
let b = 0;
println!("{}", a/b); // attempt to divide `0_i32` by zero
let a = 3;
let b = 3;
println!("{}", 9/(a-b)); // attempt to divide `9_i32` by zero
println!("{}", 0.0f64/0f64); // NaN
println!("{}", 0.1f64/0f64); // inf
println!("{}", -0.1f64/0f64); // -inf
println!("{}", 0.0f32/0f32); // NaN
println!("{}", 0.1f32/0f32); // inf
println!("{}", -0.1f32/0f32); // -inf
}
Go
go version go1.17 windows/amd64
package main
func main() {
// var a int32 = 3
// var b int32 = 3
// var c int32 = 9
// println(c / (a - b)) // 运行出错 panic: runtime error: integer divide by zero
// println(c / 0) // 编译出错 division by zero
// println(float64(0) / float64(0)) // 编译出错 division by zero
var a float64 = 0.0
println(float64(0) / a) // NaN
println(float64(0.1) / a) // +Inf
println(float64(-0.1) / a) // -Inf
var b float32 = 0.0
println(float32(0) / b) // NaN
println(float32(0.1) / b) // +Inf
println(float32(-0.1) / b) // -Inf
}
C
gcc version 4.8.5 20150623 (Red Hat 4.8.5-39) (GCC)
#include <stdio.h>
int main() {
// printf("%d\n", 0/0); // 编译警告 warning: division by zero [-Wdiv-by-zero]
int a = 0;
int b = 0;
// printf("%d\n", a/b); // 运行出错 Floating point exception
printf("%f\n", (float)0/(float)0); // -nan
printf("%f\n", (float)0.1/(float)0); // +inf
printf("%f\n", (float)-0.1/(float)0); // -inf
printf("%f\n", (double)0/(double)0); // -nan
printf("%f\n", (double)0.1/(double)0); // +inf
printf("%f\n", (double)-0.1/(double)0); // -inf
}
C++
gcc version 4.8.5 20150623 (Red Hat 4.8.5-39) (GCC)
#include <iostream>
using namespace std;
int main() {
// cout << 0 / 0 << endl; // 编译警告 warning: division by zero [-Wdiv-by-zero] 运行报错：Floating point exception
int ia = 0;
int ib = 0;
// cout << ia / ib << endl; // 运行出错：Floating point exception
cout << float(0) / float(0) << endl; // -nan
cout << float(0.1) / float(0) << endl; // +inf
cout << float(-0.1) / float(0) << endl; // -inf
cout << double(0) / double(0) << endl; // -nan
cout << double(0.1) / double(0) << endl; // +inf
cout << double(-0.1) / double(0) << endl; // -inf
}
Python
python 3.9
Python 3.9.2 (tags/v3.9.2:1a79785, Feb 19 2021, 13:44:55) [MSC v.1928 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 0/0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero
>>> 0.1/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
>>> 0.0/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
>>> -0.1/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
python 2.7
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 0/0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero
>>> 0.1/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
>>> 0.0/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
>>> -0.1/0.0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
结论
Python 的表现最好，无论是整数除 0 还是浮点除 0 都返回的错误：ZeroDivisionError。但跟编译型语言无法比较，因为无论如何，运行到的时候都挂了。
编译报错的情况：Rust 整数除 0，不论是简直还是直接，代码均编译不过，Go 直接整数除 0 会编译不通过。但是直接除浮点数 0 时，不会报编译问题，但是 Go 能正常识别，编译不过。此处 Rust 和 Go 几乎五五开。
C、C++ 直接除 0 编译器都会给出警告，但是可以运行，运行的时候报错。