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/* $Id: mul.S,v 1.1 2005-12-20 09:50:47 jcastillo Exp $

 * mul.S:       This routine was taken from glibc-1.09 and is covered

 *              by the GNU Library General Public License Version 2.

 */

/*

 * Signed multiply, from Appendix E of the Sparc Version 8

 * Architecture Manual.

 */

/*

 * Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the upper 32 bits of

 * the 64-bit product).

 *

 * This code optimizes short (less than 13-bit) multiplies.

 */

        .globl .mul

.mul:

        mov     %o0, %y         ! multiplier -> Y

        andncc  %o0, 0xfff, %g0 ! test bits 12..31

        be      Lmul_shortway   ! if zero, can do it the short way

        andcc   %g0, %g0, %o4   ! zero the partial product and clear N and V

        /*

         * Long multiply.  32 steps, followed by a final shift step.

         */

        mulscc  %o4, %o1, %o4   ! 1

        mulscc  %o4, %o1, %o4   ! 2

        mulscc  %o4, %o1, %o4   ! 3

        mulscc  %o4, %o1, %o4   ! 4

        mulscc  %o4, %o1, %o4   ! 5

        mulscc  %o4, %o1, %o4   ! 6

        mulscc  %o4, %o1, %o4   ! 7

        mulscc  %o4, %o1, %o4   ! 8

        mulscc  %o4, %o1, %o4   ! 9

        mulscc  %o4, %o1, %o4   ! 10

        mulscc  %o4, %o1, %o4   ! 11

        mulscc  %o4, %o1, %o4   ! 12

        mulscc  %o4, %o1, %o4   ! 13

        mulscc  %o4, %o1, %o4   ! 14

        mulscc  %o4, %o1, %o4   ! 15

        mulscc  %o4, %o1, %o4   ! 16

        mulscc  %o4, %o1, %o4   ! 17

        mulscc  %o4, %o1, %o4   ! 18

        mulscc  %o4, %o1, %o4   ! 19

        mulscc  %o4, %o1, %o4   ! 20

        mulscc  %o4, %o1, %o4   ! 21

        mulscc  %o4, %o1, %o4   ! 22

        mulscc  %o4, %o1, %o4   ! 23

        mulscc  %o4, %o1, %o4   ! 24

        mulscc  %o4, %o1, %o4   ! 25

        mulscc  %o4, %o1, %o4   ! 26

        mulscc  %o4, %o1, %o4   ! 27

        mulscc  %o4, %o1, %o4   ! 28

        mulscc  %o4, %o1, %o4   ! 29

        mulscc  %o4, %o1, %o4   ! 30

        mulscc  %o4, %o1, %o4   ! 31

        mulscc  %o4, %o1, %o4   ! 32

        mulscc  %o4, %g0, %o4   ! final shift

        ! If %o0 was negative, the result is

        !       (%o0 * %o1) + (%o1 << 32))

        ! We fix that here.

#if 0

        tst     %o0

        bge     1f

        rd      %y, %o0

        ! %o0 was indeed negative; fix upper 32 bits of result by subtracting

        ! %o1 (i.e., return %o4 - %o1 in %o1).

        retl

        sub     %o4, %o1, %o1

1:

        retl

        mov     %o4, %o1

#else

        /* Faster code adapted from tege@sics.se's code for umul.S.  */

        sra     %o0, 31, %o2    ! make mask from sign bit

        and     %o1, %o2, %o2   ! %o2 = 0 or %o1, depending on sign of %o0

        rd      %y, %o0         ! get lower half of product

        retl

        sub     %o4, %o2, %o1   ! subtract compensation

                                !  and put upper half in place

#endif

Lmul_shortway:

        /*

         * Short multiply.  12 steps, followed by a final shift step.

         * The resulting bits are off by 12 and (32-12) = 20 bit positions,

         * but there is no problem with %o0 being negative (unlike above).

         */

        mulscc  %o4, %o1, %o4   ! 1

        mulscc  %o4, %o1, %o4   ! 2

        mulscc  %o4, %o1, %o4   ! 3

        mulscc  %o4, %o1, %o4   ! 4

        mulscc  %o4, %o1, %o4   ! 5

        mulscc  %o4, %o1, %o4   ! 6

        mulscc  %o4, %o1, %o4   ! 7

        mulscc  %o4, %o1, %o4   ! 8

        mulscc  %o4, %o1, %o4   ! 9

        mulscc  %o4, %o1, %o4   ! 10

        mulscc  %o4, %o1, %o4   ! 11

        mulscc  %o4, %o1, %o4   ! 12

        mulscc  %o4, %g0, %o4   ! final shift

        /*

         *  %o4 has 20 of the bits that should be in the low part of the

         * result; %y has the bottom 12 (as %y's top 12).  That is:

         *

         *        %o4               %y

         * +----------------+----------------+

         * | -12- |   -20-  | -12- |   -20-  |

         * +------(---------+------)---------+

         *  --hi-- ----low-part----

         *

         * The upper 12 bits of %o4 should be sign-extended to form the

         * high part of the product (i.e., highpart = %o4 >> 20).

         */

        rd      %y, %o5

        sll     %o4, 12, %o0    ! shift middle bits left 12

        srl     %o5, 20, %o5    ! shift low bits right 20, zero fill at left

        or      %o5, %o0, %o0   ! construct low part of result

        retl

        sra     %o4, 20, %o1    ! ... and extract high part of result