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NEED FAST SIGNED DIVISION on PPLAIN

How may i be able to break a signed division by a constant

into cheaper sequences of adds (and one imul, maybe)


For unsigned division we may use the following

formula:

a/b == (int)(((2^32)+b-1)/b) * (a) / (2^32)

but does it hold for signed division?

can anyone recall michael abrash's code for doing

fast signed division. i guess he had

discussed in the mar 92 issue of Dr dobb's.




Comments

  • Why don't you use IDIV (signed) or DIV (unsigned)? It takes one clock cycle, which is really fast. On a 90mhz comp, there are 90 million clock cycles per second.

    MOV AX, 8

    MOV BX, 4

    IDIV BX (or DIV BX)

    AX now equals 2


  • : Why don't you use IDIV (signed) or DIV (unsigned)? It takes one clock cycle, which is really fast. On a 90mhz comp, there are 90 million clock cycles per second.

    : MOV AX, 8

    : MOV BX, 4

    : IDIV BX (or DIV BX)

    : AX now equals 2


    yeah but all this is good on pII or PIII

    i am looking for a PPLAIN(pentium or i586

    or whatever you may call it)

    speed up.


  • I expected some answers to my query.

    But it seems readers of this forum are more interested in

    DOS & stuffs like that.


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