Re: Rounding with Div and Mod operators

  "Scott.David.Daniels" <Scott.Daniels@Acm.Org> writes:
> One thing I'd mention is that each CPU manufacturer builds one of the
> definitions in hardware.


No. E.g., the Alpha architecture has no integer division instruction.
The 88k architecture had signed and unsigned integer division
instructions, but apparently the signed division is slow or broken on
the 88100, so signed division was synthesized out of unsigned division
in software.


> Here's an interesting question assuming a two's complement machine:
> Let MinInf = <sign bit on, all others off = most negative int = -1Q0>
> (points to those other old fogeys who know what -1Q0 means). What is
> -1 rem MinInf ?


The same for both floored and symmetric division, because the sign of
the operands is the same: -1. I tested this in Gforth (compiled with
gcc), and got the correct result for /mod, fm/mod, and sm/rem.


- anton
--
M. Anton Ertl Some things have to be seen to be believed
anton@mips.complang.tuwien.ac.at Most things have to be believed to be seen
http://www.complang.tuwien.ac.at/anton/home.html

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