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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