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/*

 * arch/alpha/lib/divide.S

 *

 * (C) 1995 Linus Torvalds

 *

 * Alpha division..

 */

/*

 * The alpha chip doesn't provide hardware division, so we have to do it

 * by hand.  The compiler expects the functions

 *

 *      __divqu: 64-bit unsigned long divide

 *      __remqu: 64-bit unsigned long remainder

 *      __divqs/__remqs: signed 64-bit

 *      __divlu/__remlu: unsigned 32-bit

 *      __divls/__remls: signed 32-bit

 *

 * These are not normal C functions: instead of the normal

 * calling sequence, these expect their arguments in registers

 * $24 and $25, and return the result in $27. Register $28 may

 * be clobbered (assembly temporary), anything else must be saved.

 *

 * In short: painful.

 *

 * This is a rather simple bit-at-a-time algorithm: it's very good

 * at dividing random 64-bit numbers, but the more usual case where

 * the divisor is small is handled better by the DEC algorithm

 * using lookup tables. This uses much less memory, though, and is

 * nicer on the cache.. Besides, I don't know the copyright status

 * of the DEC code.

 */

/*

 * My temporaries:

 *      $0 - current bit

 *      $1 - shifted divisor

 *      $2 - modulus/quotient

 *

 *      $23 - return address

 *      $24 - dividend

 *      $25 - divisor

 *

 *      $27 - quotient/modulus

 *      $28 - compare status

 */

#define halt .long 0

/*

 * Select function type and registers

 */

#define mask    $0

#define divisor $1

#define compare $28

#define tmp1    $3

#define tmp2    $4

#ifdef DIV

#define DIV_ONLY(x,y...) x,##y

#define MOD_ONLY(x,y...)

#define func(x) __div##x

#define modulus $2

#define quotient $27

#define GETSIGN(x) xor $24,$25,x

#define STACK 48

#else

#define DIV_ONLY(x,y...)

#define MOD_ONLY(x,y...) x,##y

#define func(x) __rem##x

#define modulus $27

#define quotient $2

#define GETSIGN(x) bis $24,$24,x

#define STACK 32

#endif

/*

 * For 32-bit operations, we need to extend to 64-bit

 */

#ifdef INTSIZE

#define ufunction func(lu)

#define sfunction func(l)

#define LONGIFY(x) zapnot x,15,x

#define SLONGIFY(x) addl x,0,x

#else

#define ufunction func(qu)

#define sfunction func(q)

#define LONGIFY(x)

#define SLONGIFY(x)

#endif

.set noat

.align  3

.globl  ufunction

.ent    ufunction

ufunction:

        subq    $30,STACK,$30

        .frame  $30,STACK,$23

        .prologue 0

7:      stq     $1, 0($30)

        bis     $25,$25,divisor

        stq     $2, 8($30)

        bis     $24,$24,modulus

        stq     $0,16($30)

        bis     $31,$31,quotient

        LONGIFY(divisor)

        stq     tmp1,24($30)

        LONGIFY(modulus)

        bis     $31,1,mask

        DIV_ONLY(stq tmp2,32($30))

        beq     divisor, 9f                     /* div by zero */

#ifdef INTSIZE

        /*

         * shift divisor left, using 3-bit shifts for

         * 32-bit divides as we can't overflow. Three-bit

         * shifts will result in looping three times less

         * here, but can result in two loops more later.

         * Thus using a large shift isn't worth it (and

         * s8add pairs better than a sll..)

         */

1:      cmpult  divisor,modulus,compare

        s8addq  divisor,$31,divisor

        s8addq  mask,$31,mask

        bne     compare,1b

#else

1:      cmpult  divisor,modulus,compare

        blt     divisor, 2f

        addq    divisor,divisor,divisor

        addq    mask,mask,mask

        bne     compare,1b

        unop

#endif

        /* ok, start to go right again.. */

2:      DIV_ONLY(addq quotient,mask,tmp2)

        srl     mask,1,mask

        cmpule  divisor,modulus,compare

        subq    modulus,divisor,tmp1

        DIV_ONLY(cmovne compare,tmp2,quotient)

        srl     divisor,1,divisor

        cmovne  compare,tmp1,modulus

        bne     mask,2b

9:      ldq     $1, 0($30)

        ldq     $2, 8($30)

        ldq     $0,16($30)

        ldq     tmp1,24($30)

        DIV_ONLY(ldq tmp2,32($30))

        addq    $30,STACK,$30

        ret     $31,($23),1

        .end    ufunction

/*

 * Uhh.. Ugly signed division. I'd rather not have it at all, but

 * it's needed in some circumstances. There are different ways to

 * handle this, really. This does:

 *      -a / b = a / -b = -(a / b)

 *      -a % b = -(a % b)

 *      a % -b = a % b

 * which is probably not the best solution, but at least should

 * have the property that (x/y)*y + (x%y) = x.

 */

.align 3

.globl  sfunction

.ent    sfunction

sfunction:

        subq    $30,STACK,$30

        .frame  $30,STACK,$23

        .prologue 0

        bis     $24,$25,$28

        SLONGIFY($28)

        bge     $28,7b

        stq     $24,0($30)

        subq    $31,$24,$28

        stq     $25,8($30)

        cmovlt  $24,$28,$24     /* abs($24) */

        stq     $23,16($30)

        subq    $31,$25,$28

        stq     tmp1,24($30)

        cmovlt  $25,$28,$25     /* abs($25) */

        unop

        bsr     $23,ufunction

        ldq     $24,0($30)

        ldq     $25,8($30)

        GETSIGN($28)

        subq    $31,$27,tmp1

        SLONGIFY($28)

        ldq     $23,16($30)

        cmovlt  $28,tmp1,$27

        ldq     tmp1,24($30)

        addq    $30,STACK,$30

        ret     $31,($23),1

        .end    sfunction