Languguage OS 2/Languguage OS II Version 10-94 (Knowledge Media)(1994).ISO/gnu/glibc108.zip/glibc108/sysdeps/sparc/sdiv.S

Text File | 1993-05-12 | 7KB | 366 lines

   /* This file is generated from divrem.m4; DO NOT EDIT! */
/*
 * Division and remainder, from Appendix E of the Sparc Version 8
 * Architecture Manual, with fixes from Gordon Irlam.
 */

/*
 * Input: dividend and divisor in %o0 and %o1 respectively.
 *
 * m4 parameters:
 *  .div    name of function to generate
 *  div        div=div => %o0 / %o1; div=rem => %o0 % %o1
 *  true        true=true => signed; true=false => unsigned
 *
 * Algorithm parameters:
 *  N        how many bits per iteration we try to get (4)
 *  WORDSIZE    total number of bits (32)
 *
 * Derived constants:
 *  TOPBITS    number of bits in the top decade of a number
 *
 * Important variables:
 *  Q        the partial quotient under development (initially 0)
 *  R        the remainder so far, initially the dividend
 *  ITER    number of main division loop iterations required;
 *        equal to ceil(log2(quotient) / N).  Note that this
 *        is the log base (2^N) of the quotient.
 *  V        the current comparand, initially divisor*2^(ITER*N-1)
 *
 * Cost:
 *  Current estimate for non-large dividend is
 *    ceil(log2(quotient) / N) * (10 + 7N/2) + C
 *  A large dividend is one greater than 2^(31-TOPBITS) and takes a
 *  different path, as the upper bits of the quotient must be developed
 *  one bit at a time.
 */



#include "DEFS.h"
#ifdef __svr4__
#include <sys/trap.h>
#else
#include <machine/trap.h>
#endif

FUNC(.div)
    ! compute sign of result; if neither is negative, no problem
    orcc    %o1, %o0, %g0    ! either negative?
    bge    2f            ! no, go do the divide
    xor    %o1, %o0, %g6    ! compute sign in any case
    tst    %o1
    bge    1f
    tst    %o0
    ! %o1 is definitely negative; %o0 might also be negative
    bge    2f            ! if %o0 not negative...
    sub    %g0, %o1, %o1    ! in any case, make %o1 nonneg
1:    ! %o0 is negative, %o1 is nonnegative
    sub    %g0, %o0, %o0    ! make %o0 nonnegative
2:

    ! Ready to divide.  Compute size of quotient; scale comparand.
    orcc    %o1, %g0, %o5
    bne    1f
    mov    %o0, %o3

        ! Divide by zero trap.  If it returns, return 0 (about as
        ! wrong as possible, but that is what SunOS does...).
        ta    ST_DIV0
        retl
        clr    %o0

1:
    cmp    %o3, %o5            ! if %o1 exceeds %o0, done
    blu    Lgot_result        ! (and algorithm fails otherwise)
    clr    %o2
    sethi    %hi(1 << (32 - 4 - 1)), %g1
    cmp    %o3, %g1
    blu    Lnot_really_big
    clr    %o4

    ! Here the dividend is >= 2^(31-N) or so.  We must be careful here,
    ! as our usual N-at-a-shot divide step will cause overflow and havoc.
    ! The number of bits in the result here is N*ITER+SC, where SC <= N.
    ! Compute ITER in an unorthodox manner: know we need to shift V into
    ! the top decade: so do not even bother to compare to R.
    1:
        cmp    %o5, %g1
        bgeu    3f
        mov    1, %g7
        sll    %o5, 4, %o5
        b    1b
        add    %o4, 1, %o4

    ! Now compute %g7.
    2:    addcc    %o5, %o5, %o5
        bcc    Lnot_too_big
        add    %g7, 1, %g7

        ! We get here if the %o1 overflowed while shifting.
        ! This means that %o3 has the high-order bit set.
        ! Restore %o5 and subtract from %o3.
        sll    %g1, 4, %g1    ! high order bit
        srl    %o5, 1, %o5        ! rest of %o5
        add    %o5, %g1, %o5
        b    Ldo_single_div
        sub    %g7, 1, %g7

    Lnot_too_big:
    3:    cmp    %o5, %o3
        blu    2b
        nop
        be    Ldo_single_div
        nop
    /* NB: these are commented out in the V8-Sparc manual as well */
    /* (I do not understand this) */
    ! %o5 > %o3: went too far: back up 1 step
    !    srl    %o5, 1, %o5
    !    dec    %g7
    ! do single-bit divide steps
    !
    ! We have to be careful here.  We know that %o3 >= %o5, so we can do the
    ! first divide step without thinking.  BUT, the others are conditional,
    ! and are only done if %o3 >= 0.  Because both %o3 and %o5 may have the high-
    ! order bit set in the first step, just falling into the regular
    ! division loop will mess up the first time around.
    ! So we unroll slightly...
    Ldo_single_div:
        subcc    %g7, 1, %g7
        bl    Lend_regular_divide
        nop
        sub    %o3, %o5, %o3
        mov    1, %o2
        b    Lend_single_divloop
        nop
    Lsingle_divloop:
        sll    %o2, 1, %o2
        bl    1f
        srl    %o5, 1, %o5
        ! %o3 >= 0
        sub    %o3, %o5, %o3
        b    2f
        add    %o2, 1, %o2
    1:    ! %o3 < 0
        add    %o3, %o5, %o3
        sub    %o2, 1, %o2
    2:
    Lend_single_divloop:
        subcc    %g7, 1, %g7
        bge    Lsingle_divloop
        tst    %o3
        b,a    Lend_regular_divide

Lnot_really_big:
1:
    sll    %o5, 4, %o5
    cmp    %o5, %o3
    bleu    1b
    addcc    %o4, 1, %o4
    be    Lgot_result
    sub    %o4, 1, %o4

    tst    %o3    ! set up for initial iteration
Ldivloop:
    sll    %o2, 4, %o2
        ! depth 1, accumulated bits 0
    bl    L.1.16
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 2, accumulated bits 1
    bl    L.2.17
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 3, accumulated bits 3
    bl    L.3.19
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 4, accumulated bits 7
    bl    L.4.23
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (7*2+1), %o2

L.4.23:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (7*2-1), %o2


L.3.19:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 4, accumulated bits 5
    bl    L.4.21
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (5*2+1), %o2

L.4.21:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (5*2-1), %o2



L.2.17:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 3, accumulated bits 1
    bl    L.3.17
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 4, accumulated bits 3
    bl    L.4.19
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (3*2+1), %o2

L.4.19:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (3*2-1), %o2


L.3.17:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 4, accumulated bits 1
    bl    L.4.17
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (1*2+1), %o2

L.4.17:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (1*2-1), %o2




L.1.16:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 2, accumulated bits -1
    bl    L.2.15
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 3, accumulated bits -1
    bl    L.3.15
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 4, accumulated bits -1
    bl    L.4.15
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-1*2+1), %o2

L.4.15:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-1*2-1), %o2


L.3.15:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 4, accumulated bits -3
    bl    L.4.13
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-3*2+1), %o2

L.4.13:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-3*2-1), %o2



L.2.15:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 3, accumulated bits -3
    bl    L.3.13
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
            ! depth 4, accumulated bits -5
    bl    L.4.11
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-5*2+1), %o2

L.4.11:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-5*2-1), %o2


L.3.13:
    ! remainder is negative
    addcc    %o3,%o5,%o3
            ! depth 4, accumulated bits -7
    bl    L.4.9
    srl    %o5,1,%o5
    ! remainder is positive
    subcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-7*2+1), %o2

L.4.9:
    ! remainder is negative
    addcc    %o3,%o5,%o3
        b    9f
        add    %o2, (-7*2-1), %o2




    9:
Lend_regular_divide:
    subcc    %o4, 1, %o4
    bge    Ldivloop
    tst    %o3
    bl,a    Lgot_result
    ! non-restoring fixup here (one instruction only!)
    sub    %o2, 1, %o2


Lgot_result:
    ! check to see if answer should be < 0
    tst    %g6
    bl,a    1f
    sub %g0, %o2, %o2
1:
    retl
    mov %o2, %o0