awk算数运算的疑问

murdercool

1. awk 'BEGIN{a=(0.9-0.8)*10;print a;if(a==1){print "yes"}else{print "N"}}'
   
2. 1
   
3. N
   
4. 
   
5. awk 'BEGIN{a=(0.9-0.8)*10;print a;if(a<1){print "yes"}else{print "N"}}'
   
6. 1
   
7. yes
   

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这里a是等于1的啊，为什么判断<1 反倒为真呢。。求解释

代号：军刀

贴在代码框里

jason680

回复 1# murdercool

http://zh.wikipedia.org/zh-cn/IEEE_754
IEEE二进制浮点数算术标准（IEEE 754）是1980年代以来最广泛使用的浮点数运算标准，为许多CPU与浮点运算器所采用。...

murdercool

回复 3# jason680


    怎么解决呢

reyleon

1. awk 'BEGIN{a=(0.9-0.8)*10;print a;if(a=="1"){print "yes"}else{print "N"}}'

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jason680

回复 4# murdercool

1. using awk, but don't using float
Note: change some algorithm

$ awk 'BEGIN{n=(0.9-0.8)*10;print n;if(n==1){print "yes"}else{print "No"}}'
1
No


$ awk 'BEGIN{n=0.9*10-0.8*10;print n;if(n==1){print "yes"}else{print "No"}}'
1
yes

2. using awk with error(误差)
Note: using the same algorithm and using some function to check equal

$ awk 'function eq(n,m,err,diff){diff=(n>m)?n-m:m-n;return diff<=err?1:0}BEGIN{n=(0.9-0.8)*10;printf("%.20f\n",n);if(eq(n,1,0.00000000000001)){print "yes"}else{print "No"}}'
0.99999999999999977796
yes


$ awk 'function eq(n,m,err,diff){diff=(n>m)?n-m:m-n;return diff<=err?1:0}BEGIN{n=(0.9-0.8)*10;printf("%.20f\n",n);if(eq(n,1,0.000000000000000001)){print "yes"}else{print "No"}}'
0.99999999999999977796
No

3. using other language(ex: perl) to support it
Note: using the same algorithm

$ perl -e 'use bignum; $n=(0.9-0.8)*10;printf("%.20f\n",$n);if($n==1){print "yes\n"}else{print "No\n"}'
1.00000000000000000000
yes

$ perl -e '$n=(0.9-0.8)*10;printf("%.20f\n",$n);if($n==1){print "yes\n"}else{print "No\n"}'
0.99999999999999977796
No
   

yestreenstars

回复 6# jason680


学习了，没想到a=(0.9-0.8)*10用printf("%.20f\n",a)打印出来的效果是这样的！

murdercool

回复 6# jason680
   
     谢谢！！ 刚试了下

1. awk 'BEGIN{a=(0.9-0.8)*10;print a;if(a eq 1){print "yes"}else{print "N"}}'
   
2. 1
   
3. yes

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貌似有eq内置函数 ，以前还真没看到过

yestreenstars

回复 8# murdercool


    在awk里没有eq这个内置函数，不信你把1换成2、3、4……结果都是yes。

murdercool

回复 9# yestreenstars


   是的，   我2了  :wink: