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>As far as I know, the GSL (Gnu
>Scientific Library) provides full support of the rounding
>options of the FPU.
>
>You might check their C code to get some clues.
Bernhard
Thanks for the clues. I have found some nice test examples
which (hopefully) will be useful.
The required control words are also clearly documented:
/* Here is the dirty part. Set up your 387 through the control word
* (cw) register.
*
* 15-13 12 11-10 9-8 7-6 5 4 3 2 1 0
* | reserved | IC | RC | PC | reserved | PM | UM | OM | ZM | DM | IM
*
* IM: Invalid operation mask
* DM: Denormalized operand mask
* ZM: Zero-divide mask
* OM: Overflow mask
* UM: Underflow mask
* PM: Precision (inexact result) mask
*
* Mask bit is 1 means no interrupt.
*
* PC: Precision control
* 11 - round to extended precision
* 10 - round to double precision
* 00 - round to single precision
*
* RC: Rounding control
* 00 - rounding to nearest
* 01 - rounding down (toward - infinity)
* 10 - rounding up (toward + infinity)
* 11 - rounding toward zero
*
* IC: Infinity control
* That is for 8087 and 80287 only.
*
* The hardware default is 0x037f which we use.
*/
I have also found the C code to do it:
/* Macros for accessing the hardware control word. */
#define _FPU_GETCW(cw) __asm__ ("fnstcw %0" : "=m" (*&cw))
#define _FPU_SETCW(cw) __asm__ ("fldcw %0" : : "m" (*&cw))
However I have never leaned to read (or write) C so I
do not know how to translate the two lines above. Any
ideas anyone ?
The example below is the kind of thing I am hoping to end up
with.
PROCEDURE [code] MultMod* (a, b, m : INTEGER) : INTEGER
05AH, (* pop b -> edx *)
059H, (* pop m -> ecx *)
0F7H, 0EAH, (* edx:eax := eax * edx = a * b *)
0F7H, 0F9H, (* eax := edx:eax / ecx = a * b DIV m *)
(* edx = a * b MOD m *)
08BH, 0C2H; (* move eax, edx edx -> eax *)
(*
PROCEDURE MultMod* (a, b, m : INTEGER) : INTEGER;
BEGIN
RETURN SHORT (LONG (a) * LONG (b) MOD LONG (m))
END MultMod;
*)
Thanks
Robert Campbell.
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Received on Wed Jun 19 2002 - 12:20:03 UTC