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Forum Index : Microcontroller and PC projects : PicoMite: Floating Point Quirk?
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DrifterNL Regular Member  Joined: 27/09/2018 Location: NetherlandsPosts: 58 |
Hi all, I've been trying to wrap my head around this. Is this one of those floating point quirks, is my thinking wrong or am I getting something mixed up?: * PicoMite Version 5.0706 Dim a = 100 Dim b = 0 Dim c = 0.1 start: Print b If b = a Then GoTo equ If b > a Then GoTo gre If b < a Then Inc b,c GoTo start equ: Print "equal" Print "a= " a Print "b= " b End gre: Print "greater than" Print "a= " a Print "b= " b End If I run the program as is I get: greater than a= 100 b= 100.1 b = a isn't recognized? ------------------------------------------ When I change c to 0.2 I get: greater than a= 100 b= 100 b is greater then a? ------------------------------------------ When I change c to 0.25 I get: equal a= 100 b= 100 b = a is recognized, seems to work Edited 2023-04-21 20:00 by DrifterNL Floating Point Keeps Sinking Me! Back To Integer So I Don't Get Injured. |
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| Volhout Guru  Joined: 05/03/2018 Location: NetherlandsPosts: 4253 |
Option default float ? Yes, this is strange. As if behind the comma, there is a difference that is not printed on screen. Volhout Edited 2023-04-21 20:13 by Volhout PicomiteVGA PETSCII ROBOTS |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9133 |
This is standard floating point behaviour 0.1 cannot be exactly expressed as a float therefore 1000*0.1 will not equal 100. In general you should never test for equality of floats after any arithmetic but must allow a small delta e.g. if abs(a-b)<0.000000001 |
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| DrifterNL Regular Member Joined: 27/09/2018 Location: NetherlandsPosts: 58 |
Thanks for the info! Darn, floating point got me again.  Floating Point Keeps Sinking Me! Back To Integer So I Don't Get Injured. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2079 |
Think I might have mentioned this before, Years ago HiSoft BASIC had the == operator which meant "roughly equal to" precisely because of FP wrinkles like this so IF 1000*0.1 == 100 would be true no idea how the thresholds were set up As a callow youth taking my first steps in this stuff professionally, It was always drummed into us to "get things into integer ASAP" |
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