Qbasicnews.com
"idiv"ing double words - Printable Version

+- Qbasicnews.com (http://qbasicnews.com/newforum)
+-- Forum: QBasic (http://qbasicnews.com/newforum/forum-4.html)
+--- Forum: QB Discussion & Programming Help (http://qbasicnews.com/newforum/forum-11.html)
+--- Thread: "idiv"ing double words (/thread-4381.html)

"idiv"ing double words - rCX - 07-28-2004

I'm stuck Sad

Awhile back I asked if there was a way to divide dx:ax by bx and get a double word anwer. (like FFFFFFFFh / Ah = 19999999h) and I got this peice of code.....

Code:
;*dx:ax/bx; dx:ax = answer, cx = remainder*
push ax            ;save ax (lower word)
mov ax,dx        ;higher word into ax so it can be divided
xor dx,dx        ;dx = 0
div bx            ;dx:ax/bx; ax = answer dx = remainder
mov cx,ax        ;save higher word
pop ax            ;get ax, the lower word
div bx            ;dx:ax/bx again
xchg dx,cx        ;extange;dx = higher word cx = remainder

I was wondering if anyone knew how to do the same thing with the "idiv" (divide with sign) function. Thanks.

"idiv"ing double words - DrV - 07-29-2004

If that code above is correct (too lazy to check it now), just replace div with idiv.

"idiv"ing double words - rCX - 07-31-2004

Sorry I took so long....
I got this piece of code to work most of the time but when I tried to divide 6 0000h by Ah or 6 0000h by FFF6 (-Ah) I get a divide overflow error.
Code:
;Register        Function
;dx:ax    dividend (number to be divided)
;bx        divisor (number dividend is divided by)
;
;dx:ax/bx     dx:ax = answer, cx = remainder
push ax        ;save ax (lower word)
mov ax,dx    ;higher word into ax so it can be divided
cwd              ;convert dx:ax to word
idiv bx          ;dx:ax/bx; ax = answer dx = remainder
mov cx,ax        ;save higher word
pop ax         ;get ax, the lower word
idiv bx          ;dx:ax/bx again
xchg dx,cx    ;extange;dx = higher word cx = remainder


"idiv"ing double words - relsoft - 08-01-2004

Why not try to do a:

Code:
Cwde
Cdq
Movsx ebx, bx
idiv ebx

instead of a

Code:
cwd
idiv bx

Dunno if you can use extended regs though. :*)

"idiv"ing double words - rCX - 08-02-2004

I'm using DEBUG.exe I can't use double words... Sad

"idiv"ing double words - Plasma - 08-02-2004

http://www.aogosoft.com/download/debug32.rar