ESP8266 Community Forum

- Wed Dec 10, 2014 6:14 am #4480 Well, bc says -1000%10000 is -1000.
Google says: (-1000) modulo 10 000 = 9000
Wolfram Alpha says: (-1000) mod 10000 = 9000

So 2 out of three cats...

- Wed Dec 10, 2014 8:42 am #4499

(-1000) mod 10000 = 9000

The correct answer is always 9000. Modulo has a strict mathematical definition.
To move to -1000 from an arbitrary modulo zero position (say 10000) involves two retrograde steps of 10,000 and the last step has a remainder of 9000. The result of a Modulo operation is the remainder.
Coders often see coding as a mathematical skill often times they just don't get mathematics. Rounding is a good example.
When changing base notation from decimal to binary except for numbers that can be expressed as a power series in the number two there is a mathematical difference.
Coders call this rounding. It is not it is just that binary notation to a specific precision is different than decimal. EX 1/10 is 0.1 in decimal but can't be notated in binary with limited precision.
1/3 in decimal is an equivalent example .
Now coders using a handheld calculator are sometimes unaware that the calculator uses binary coded decimal so never is base conversion an issue.

- Wed Dec 10, 2014 8:53 am #4500

The correct answer is always 9000. Modulo has a strict mathematical definition.
To move to -1000 from an arbitrary modulo zero position (say 10000) involves two retrograde steps of 10,000 and the last step has a remainder of 9000. The result of a Modulo operation is the remainder.

Thanks, the same thing occured to me in the morning - was playing with the script (and running back and forth to freezer with the sensor) until midnight

- Wed Dec 10, 2014 9:55 am #4503

(-1000) mod 10000 = 9000

The issue here is that with (-1000) the - is an infix operation it only sets the sign. Now

-(1000 mod 10000)

is different in that the bracket causes the mod to operate on 1000 prior to infix setting the sign.