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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

#ifdef DIV
#define func(x) __div##x
#define modulus $2
#define quotient $27
#define GETSIGN(x) xor $24,$25,x
#else
#define func(x) __rem##x
#define modulus $27
#define quotient $2
#define GETSIGN(x) bis $24,$24,x
#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
.globl  ufunction
.ent    ufunction
ufunction:
        subq    $30,32,$30
        stq     $0, 0($30)
        stq     $1, 8($30)
        stq     $2,16($30)

        bis     $25,$25,divisor
        bis     $24,$24,modulus
        bis     $31,$31,quotient
        LONGIFY(divisor)
        LONGIFY(modulus)
        beq     divisor, 9f                     /* div by zero */
        bis     $31,1,mask

        /* shift divisor left */
1:      cmpult  divisor,modulus,compare
        blt     divisor, 3f
        addq    divisor,divisor,divisor
        addq    mask,mask,mask
        bne     compare,1b

        /* ok, start to go right again.. */
2:      srl     divisor,1,divisor
        beq     mask,9f
        srl     mask,1,mask
3:      cmpule  divisor,modulus,compare
        beq     compare,2b
        addq    quotient,mask,quotient
        beq     mask,9f
        subq    modulus,divisor,modulus
        br      2b

9:      ldq     $0, 0($30)
        ldq     $1, 8($30)
        ldq     $2, 16($30)
        addq    $30,32,$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.
 */
.globl  sfunction
.ent    sfunction
sfunction:
        bis     $24,$25,$28
        SLONGIFY($28)
        bge     $28,ufunction
        subq    $30,32,$30
        stq     $23,0($30)
        stq     $24,8($30)
        stq     $25,16($30)
        subq    $31,$24,$28
        cmovlt  $24,$28,$24     /* abs($24) */
        subq    $31,$25,$28
        cmovlt  $25,$28,$25     /* abs($25) */
        bsr     $23,ufunction
        ldq     $23,0($30)
        ldq     $24,8($30)
        ldq     $25,16($30)
        addq    $30,32,$30
        GETSIGN($28)
        SLONGIFY($28)
        bge     $28,1f
        subq    $31,$27,$27
1:      ret     $31,($23),1
        .end    sfunction