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/*---------------------------------------------------------------------------+
 |  polynomial_Xsig.S                                                        |
 |                                                                           |
 | Fixed point arithmetic polynomial evaluation.                             |
 |                                                                           |
 | Copyright (C) 1992,1993,1994,1995                                         |
 |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
 |                       Australia.  E-mail billm@jacobi.maths.monash.edu.au |
 |                                                                           |
 | Call from C as:                                                           |
 |   void polynomial_Xsig(Xsig *accum, unsigned long long x,                 |
 |                        unsigned long long terms[], int n)                 |
 |                                                                           |
 | Computes:                                                                 |
 | terms[0] + (terms[1] + (terms[2] + ... + (terms[n-1]*x)*x)*x)*x) ... )*x  |
 | and adds the result to the 12 byte Xsig.                                  |
 | The terms[] are each 8 bytes, but all computation is performed to 12 byte |
 | precision.                                                                |
 |                                                                           |
 | This function must be used carefully: most overflow of intermediate       |
 | results is controlled, but overflow of the result is not.                 |
 |                                                                           |
 +---------------------------------------------------------------------------*/
        .file   "polynomial_Xsig.S"

#include "fpu_emu.h"


#define TERM_SIZE       $8
#define SUM_MS          -20(%ebp)       /* sum ms long */
#define SUM_MIDDLE      -24(%ebp)       /* sum middle long */
#define SUM_LS          -28(%ebp)       /* sum ls long */
#define ACCUM_MS        -4(%ebp)        /* accum ms long */
#define ACCUM_MIDDLE    -8(%ebp)        /* accum middle long */
#define ACCUM_LS        -12(%ebp)       /* accum ls long */
#define OVERFLOWED      -16(%ebp)       /* addition overflow flag */

.text
ENTRY(polynomial_Xsig)
        pushl   %ebp
        movl    %esp,%ebp
        subl    $32,%esp
        pushl   %esi
        pushl   %edi
        pushl   %ebx

        movl    PARAM2,%esi             /* x */
        movl    PARAM3,%edi             /* terms */

        movl    TERM_SIZE,%eax
        mull    PARAM4                  /* n */
        addl    %eax,%edi

        movl    4(%edi),%edx            /* terms[n] */
        movl    %edx,SUM_MS
        movl    (%edi),%edx             /* terms[n] */
        movl    %edx,SUM_MIDDLE
        xor     %eax,%eax
        movl    %eax,SUM_LS
        movb    %al,OVERFLOWED

        subl    TERM_SIZE,%edi
        decl    PARAM4
        js      L_accum_done

L_accum_loop:
        xor     %eax,%eax
        movl    %eax,ACCUM_MS
        movl    %eax,ACCUM_MIDDLE

        movl    SUM_MIDDLE,%eax
        mull    (%esi)                  /* x ls long */
        movl    %edx,ACCUM_LS

        movl    SUM_MIDDLE,%eax
        mull    4(%esi)                 /* x ms long */
        addl    %eax,ACCUM_LS
        adcl    %edx,ACCUM_MIDDLE
        adcl    $0,ACCUM_MS

        movl    SUM_MS,%eax
        mull    (%esi)                  /* x ls long */
        addl    %eax,ACCUM_LS
        adcl    %edx,ACCUM_MIDDLE
        adcl    $0,ACCUM_MS

        movl    SUM_MS,%eax
        mull    4(%esi)                 /* x ms long */
        addl    %eax,ACCUM_MIDDLE
        adcl    %edx,ACCUM_MS

        testb   $0xff,OVERFLOWED
        jz      L_no_overflow

        movl    (%esi),%eax
        addl    %eax,ACCUM_MIDDLE
        movl    4(%esi),%eax
        adcl    %eax,ACCUM_MS           /* This could overflow too */

L_no_overflow:

/*
 * Now put the sum of next term and the accumulator
 * into the sum register
 */
        movl    ACCUM_LS,%eax
        addl    (%edi),%eax             /* term ls long */
        movl    %eax,SUM_LS
        movl    ACCUM_MIDDLE,%eax
        adcl    (%edi),%eax             /* term ls long */
        movl    %eax,SUM_MIDDLE
        movl    ACCUM_MS,%eax
        adcl    4(%edi),%eax            /* term ms long */
        movl    %eax,SUM_MS
        sbbb    %al,%al
        movb    %al,OVERFLOWED          /* Used in the next iteration */

        subl    TERM_SIZE,%edi
        decl    PARAM4
        jns     L_accum_loop

L_accum_done:
        movl    PARAM1,%edi             /* accum */
        movl    SUM_LS,%eax
        addl    %eax,(%edi)
        movl    SUM_MIDDLE,%eax
        adcl    %eax,4(%edi)
        movl    SUM_MS,%eax
        adcl    %eax,8(%edi)

        popl    %ebx
        popl    %edi
        popl    %esi
        leave
        ret