This is really strange that i’m getting a negative answer for this: 10^19 * 10^-18 Output: -8.446744073709551

I think it’s the third time in a week that I’m wheeling out this classic thread: [image] Discussion about integer overflow Internals & Design Yes, it is a limitation but I would not call it big since we could use BigInt if Int64 is not enough and an overflow is something…

Crap, you beat me to it. But on second thought, I think the documentation about overflow ( Integers and Floating-Point Numbers · The Julia Language ) might be more informative and less scary than a whole thread discussing whether or not it is justified?

Thank you for your help . :slight_smile:

What’s the performance hit of SaferIntegers.jl these days? Based on simple tests on my machine it seems negligible. I hope one day we can make that the default, and let people use @fastmath or similar to allow silent overflows.

For this remark the link posted by @nilshg is actually very appropriate :wink: TLDR: it’s unlikely to change (EDIT: at least anytime soon)

import BenchmarkTools: @btime import SaferIntegers: SafeInt64 n = 100_000_000 x_unsafe = fill(Int64(1), n) x_safe = fill(SafeInt64(1), n) @btime sum($x_unsafe) @btime sum($x_safe) julia> @btime sum($x_unsafe) 12.807 ms (0 allocations: 0 bytes) 100000000 julia> @btime sum($x_safe) 34.277 ms …

Not sure about this TLDR: the discussion ends on a note that Int^Int will probably become the default (while a general solution would be more difficult to implement). But it’s true the discussion in the related PR makes that seem unlikely. Also the FAQ says checked arithmetic everywhere […] ends…

[image] johnmyleswhite: The penalty seems like 3x perf regression. We’ve discussed this in the past ( julia#21600 ), and it was argued that (1) Int exponentiation is rarely performance-sensitive, and (2) there may be faster ways to check for overflow (especially for the literal powers that you…

Ouch that’s a huge hit! I was testing with the first example on SaferIntegers.jl’s homepage and got no significant difference: julia> hundredths( (@belapsed test(n, +, $sa, $sb, $sc, $sd)) / (@belapsed test(n, +, $a, $b, $c, $d)) ) 1.0

Multiplication issue

New to Julia

nilshg May 17, 2023, 8:34am 2

I think it’s the third time in a week that I’m wheeling out this classic thread:

3 Likes

Topic		Replies	Views
Julia messes up integer exponents? Performance integer-overflow	106	7351	February 21, 2019
A plea for int overflow checking as the default Internals & Design question , proposal , integer-overflow	80	12316	December 17, 2021
Potential solution to the overflow problem; 64-bit considered harmful, 32- or 21-bit better General Usage integer-overflow	6	3784	October 18, 2021
Error for 396^n General Usage bug , error	8	592	February 12, 2024
Integer power of large Integer returning very wrong results General Usage base	7	581	May 15, 2023

Multiplication issue

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