constant 256 overflows byte

[Eric Brown]

memoryBlock := make([]byte, 4)                                                                   
binary.LittleEndian.PutUint32(memoryBlock, 12345678)                                             
                                                                                                 
memoryBlock[2] = 256 - (187 - memoryBlock[2])     ' results in error: constant 256 overflows byte
memoryBlock[2] = 255 - (187 - memoryBlock[2]) + 1 ' results in no errors                         

Why is this, and what would be your suggested method of handling this?
I don't like having to do the later as it just looks sloppy.

[Eric Brown]

By the way, this is code snipped from within a conditional check, so memoryBlock[2] will always be < 187 in this situation.

[Ayan George]

On 03/07/2017 07:06 PM, Eric Brown wrote:
> memoryBlock[2] = 256 - (187 - memoryBlock[2]) ' results in error:
> constant 256 overflows byte

So since you're assigning to a byte I think Go is treating all of the
constants as bytes. A byte can only encode between 0 and 255. You need
an extra bit (ie, more than a byte) to store 256. Something like the
following works but might be silly:

memoryBlock[2] = byte(int(256) - (187 - int(memoryBlock[2])))

[Ayan George]

On 03/07/2017 07:06 PM, Eric Brown wrote:

> By the way, this is code snipped from within a conditional check, so
> memoryBlock[2] will always be < 187 in this situation.
>
> On Tuesday, March 7, 2017 at 6:02:59 PM UTC-6, Eric Brown wrote:
>
> memoryBlock := make([]byte, 4)
> binary.LittleEndian.PutUint32(memoryBlock, 12345678)
>
> memoryBlock[2] = 256 - (187 - memoryBlock[2]) ' results in error:
> constant 256 overflows byte
> memoryBlock[2] = 255 - (187 - memoryBlock[2]) + 1 ' results in no
> errors
>

Sorry, I only needed to cast the variable:

memoryBlock[2] = byte(256 - (187 - int(memoryBlock[2])))

[Eric Brown]

Thanks for the reply, Ayan.  I thought so too; however, I previously tried this... and it resulted in the same error.

[Eric Brown]

Actually, I didn't catch the int() in your example.  I tried it, and it worked!  Thank you...

[Marvin Stenger]

memoryBlock[2] += (256-187)

[Paul Hankin]

Byte operations work modulo 256, so adding 256 does nothing.

Using that, you can simplify your expression to this:

memoryBlock[2] -= 187

https://play.golang.org/p/5ljs4wIeq9

 -- 

Paul Hankin