[fpc-devel] Signed division

[J. Gareth Moreton]

Aah, thank you. That clears things up. 
Hooray for documentation! It's the same as 
suspected and listed below.

(and I noticed a mistake. I meant to say 
only if the numerator (left-hand side 
operand) is negative, not positive) 

Gareth aka. Kit

On Fri 01/06/18 12:42 , "Christo Crause" 
christo.crause at gmail.com sent:
> On Fri, Jun 1, 2018 at 11:13 AM, J. 
Gareth Moreton  wrote:
> Hi everyone,
> 
> I'm starting to make some modifications 
to the optimizer so it optimises
> div and mod operations on signed 
integers (I've done unsigned integers
> already). One question that I've 
stumbled across... what are the rules
> regarding the sign of the result?  
Experimenting with IDIV suggests it
> returns a negative modulus only if the 
numerator is positive (so -28 / 3 =
> -9 remainder -1, and -28 / -3 = 9 
remainder -1, but 28 / -3 = -9 remainder
> +1), which follows the Euclidean 
division rule of n = dq + r, where n is
> the numerator, d is the divisor, q is 
the resultant quotient and r is the
> resultant remainder.
> 
> While I'm planning on being consistent 
with IDIV, what are the rules of
> signed division in Free Pascal? There 
are hints that some dialects of
> Pascal only return a positive modulus no 
matter what.
> 
> Gareth aka. Kit
> 
>   "  The sign of the result of a Mod  
operator is the same as the sign
> of the left side operand of the Mod  
operator "
> - https://freepascal.org/docs-
html/current/ref/refsu45.html [1]  
> 
> Links:
> ------
> [1] https://freepascal.org/docs-
html/current/ref/refsu45.html
> 
>