awk算數(shù)運(yùn)算的疑問

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
   

復(fù)制代碼

這里a是等于1的啊，為什么判斷<1 反倒為真呢。。求解釋

代號(hào)：軍刀

貼在代碼框里

jason680

回復(fù) 1# murdercool

http://zh.wikipedia.org/zh-cn/IEEE_754
IEEE二進(jìn)制浮點(diǎn)數(shù)算術(shù)標(biāo)準(zhǔn)（IEEE 754）是1980年代以來最廣泛使用的浮點(diǎn)數(shù)運(yùn)算標(biāo)準(zhǔn)，為許多CPU與浮點(diǎn)運(yùn)算器所采用。...

murdercool

回復(fù) 3# jason680


    怎么解決呢

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

回復(fù) 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(誤差)
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

回復(fù) 6# jason680


學(xué)習(xí)了，沒想到a=(0.9-0.8)*10用printf("%.20f\n",a)打印出來的效果是這樣的！

murdercool

回復(fù) 6# jason680
   
     謝謝��！ 剛試了下

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內(nèi)置函數(shù) ，以前還真沒看到過

yestreenstars

回復(fù) 8# murdercool


    在awk里沒有eq這個(gè)內(nèi)置函數(shù)，不信你把1換成2、3、4……結(jié)果都是yes。

murdercool

回復(fù) 9# yestreenstars


   是的，   我2了  :wink: