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Active Forums => QB64 Discussion => Topic started by: SMcNeill on January 06, 2019, 11:54:44 am

Title: Wiki notation glitch
Post by: SMcNeill on January 06, 2019, 11:54:44 am: Making my little NumType function, I noticed a few little glitches in the wiki:

http://qb64.org/wiki/Variable_Types

If you'll look close, you'll see the min/max values for SINGLE/DOUBLE/_FLOAT:
-2.802597E-45
-4.490656458412465E-324
-1.18E−4932

These are all wrong -- obviously wrong, if one only takes a moment to think about them...

1E-2 translates to become 0.01
1E-3 becomes 0.001
1E-4 becomes 0.0001

So E-45 is VERY close to 0, and E-4932 is even closer to 0...

SINGLE and such doesn't run from 0 to limit... They run from a large negative number to a large positive number.

Those negative signs AFTER the "E" need to either all disappear, or else become "+" signs instead.

***************

Same fix needed for the charts on the DATA TYPES page as well: http://qb64.org/wiki/Data_types
Title: Re: Wiki notation glitch
Post by: Pete on January 06, 2019, 12:41:17 pm: Interesting but not something I ever studied...

So with this

a = -2.1E-45
PRINT a
a = -2.11E-45
PRINT a: END

a = -1.401298E-45
a = -2.802597E-45 (That's the lowest value as printed in the WIKI.)

If E-46 is used, the value is out of bounds and returns as zero; however, if a = 2.802598 is used, it still outputs the value of -2.802597E-45.

I guess I'm just happy I don't have anything I use that tests these boundaries.

Pete

OK, so since I still have some old QBasic books on the shelves...

Max Min
Integers: 32,767 -32,768
Long Integers: 2,147,483,647 -2,147,483,648
+Single Precision: 3.402823 E+38 1.401298 E-45
-Single Precision: -1.401298 E-45 -3.402823 E+38
+Double Precision: 1.797693134862315 D+308 4.9406564584412465 D-324
-Double Precision: -4.9406564584412465 D-324 -1.797693134862315 D+308

The WIKI differs in Single Precision, which is listed as -2.802597E-45 instead of the MS QB book limit of -1.401298 E-45

I don't have a copy of QB45 running right now, or I'd test my code above to see if it gave a different output.

Edited to change -32,767 to correct value of -32,768. Thanks RonB.
Title: Re: Wiki notation glitch
Post by: SMcNeill on January 06, 2019, 01:20:31 pm: So SINGLE is basically from: -3.402823 E+38 to +3.402823 E+38 for absolute min/max value, with greatest precision to zero being -1.401298 E-45 to +1.401298 E-45...
Title: Re: Wiki notation glitch
Post by: RhoSigma on January 06, 2019, 01:27:13 pm: It's basically what you find on the web when searching for IEEE 754...
Title: Re: Wiki notation glitch
Post by: RonB on January 06, 2019, 02:45:53 pm: Sorry, I can't resist...
The (16-bit) Integer Minimum Value should be -32768 not -32767. Prove it yourself:
a% = -32767
PRINT a% ' will show -32767
a% = a% -1
PRINT a% ' will show -32768
a% = a% -1
PRINT a% ' will show (positive) 32767 as it should
Title: Re: Wiki notation glitch
Post by: FellippeHeitor on January 06, 2019, 03:04:04 pm: Quote from: RonB on January 06, 2019, 02:45:53 pm
Sorry, I can't resist...
The (16-bit) Integer Minimum Value should be -32768 not -32767. Prove it yourself:
a% = -32767
PRINT a% ' will show -32767
a% = a% -1
PRINT a% ' will show -32768
a% = a% -1
PRINT a% ' will show (positive) 32767 as it should

True. But that's not wrong in the wiki.
Title: Re: Wiki notation glitch
Post by: Pete on January 06, 2019, 03:20:42 pm: Corrected that "typo" in the MS-QB chart I posted above. It is correct in the book. In all fairness, I'm over twice the age of that book, but I have a harder cover!

Pete
Title: Re: Wiki notation glitch
Post by: FellippeHeitor on January 06, 2019, 03:25:14 pm: There:

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Title: Re: Wiki notation glitch
Post by: Pete on January 06, 2019, 03:30:44 pm: But my chart's prettier, 'cause it's homemade.

Pete :D
Title: Re: Wiki notation glitch
Post by: FellippeHeitor on January 06, 2019, 03:41:33 pm: My horse is amazing.
Title: Re: Wiki notation glitch
Post by: SMcNeill on January 06, 2019, 03:54:24 pm: Quote from: FellippeHeitor on January 06, 2019, 03:25:14 pm
There:

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The difference here and the wiki is the +/- in the picture...

Singles goes from -3.4E38 to -1.4E-45, and then from +1.4E+45 to +3.4E+38...

It’s from a large negative number, to almost zero, and then from almost zero to a large positive number.

The way the wiki is wrote, it seems as if this would work:

IF value >= -1.4E-45 AND value <= 3.4E38 THEN value_type = SINGLE

Only problem with that: value = -128 — by the boundaries above, value wouldn’t be a valid SINGLE. -128 is < -1.4E-45...
Title: Re: Wiki notation glitch
Post by: Pete on January 06, 2019, 05:08:17 pm: Quote from: FellippeHeitor on January 06, 2019, 03:41:33 pm
My horse is amazing.

:D :D :D