Subversion Repositories openrisc_2011-10-31

//
//      $Id: scale.S,v 1.2 2001-09-27 12:01:22 chris Exp $
//
//      scale.sa 3.3 7/30/91
//
//      The entry point sSCALE computes the destination operand
//      scaled by the source operand.  If the absolute value of
//      the source operand is (>= 2^14) an overflow or underflow
//      is returned.
//
//      The entry point sscale is called from do_func to emulate
//      the fscale unimplemented instruction.
//
//      Input: Double-extended destination operand in FPTEMP, 
//              double-extended source operand in ETEMP.
//
//      Output: The function returns scale(X,Y) to fp0.
//
//      Modifies: fp0.
//
//      Algorithm:
//              
//              Copyright (C) Motorola, Inc. 1990
//                      All Rights Reserved
//
//      THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
//      The copyright notice above does not evidence any  
//      actual or intended publication of such source code.

//SCALE    idnt    2,1 | Motorola 040 Floating Point Software Package

        |section        8

#include "fpsp.defs"

        |xref   t_ovfl2
        |xref   t_unfl
        |xref   round
        |xref   t_resdnrm

SRC_BNDS: .short        0x3fff,0x400c

//
// This entry point is used by the unimplemented instruction exception
// handler.
//
//
//
//      FSCALE
//
        .global sscale
sscale:
        fmovel          #0,%fpcr                //clr user enabled exc
        clrl            %d1
        movew           FPTEMP(%a6),%d1 //get dest exponent
        smi             L_SCR1(%a6)     //use L_SCR1 to hold sign
        andil           #0x7fff,%d1     //strip sign
        movew           ETEMP(%a6),%d0  //check src bounds
        andiw           #0x7fff,%d0     //clr sign bit
        cmp2w           SRC_BNDS,%d0
        bccs            src_in
        cmpiw           #0x400c,%d0     //test for too large
        bge             src_out
//
// The source input is below 1, so we check for denormalized numbers
// and set unfl.
//
src_small:
        moveb           DTAG(%a6),%d0
        andib           #0xe0,%d0
        tstb            %d0
        beqs            no_denorm
        st              STORE_FLG(%a6)  //dest already contains result
        orl             #unfl_mask,USER_FPSR(%a6) //set UNFL
den_done:
        leal            FPTEMP(%a6),%a0
        bra             t_resdnrm
no_denorm:
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0        //simply return dest
        rts


//
// Source is within 2^14 range.  To perform the int operation,
// move it to d0.
//
src_in:
        fmovex          ETEMP(%a6),%fp0 //move in src for int
        fmovel          #rz_mode,%fpcr  //force rz for src conversion
        fmovel          %fp0,%d0                //int src to d0
        fmovel          #0,%FPSR                //clr status from above
        tstw            ETEMP(%a6)      //check src sign
        blt             src_neg
//
// Source is positive.  Add the src to the dest exponent.
// The result can be denormalized, if src = 0, or overflow,
// if the result of the add sets a bit in the upper word.
//
src_pos:
        tstw            %d1             //check for denorm
        beq             dst_dnrm
        addl            %d0,%d1         //add src to dest exp
        beqs            denorm          //if zero, result is denorm
        cmpil           #0x7fff,%d1     //test for overflow
        bges            ovfl
        tstb            L_SCR1(%a6)
        beqs            spos_pos
        orw             #0x8000,%d1
spos_pos:
        movew           %d1,FPTEMP(%a6) //result in FPTEMP
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0        //write result to fp0
        rts
ovfl:
        tstb            L_SCR1(%a6)
        beqs            sovl_pos
        orw             #0x8000,%d1
sovl_pos:
        movew           FPTEMP(%a6),ETEMP(%a6)  //result in ETEMP
        movel           FPTEMP_HI(%a6),ETEMP_HI(%a6)
        movel           FPTEMP_LO(%a6),ETEMP_LO(%a6)
        bra             t_ovfl2

denorm:
        tstb            L_SCR1(%a6)
        beqs            den_pos
        orw             #0x8000,%d1
den_pos:
        tstl            FPTEMP_HI(%a6)  //check j bit
        blts            nden_exit       //if set, not denorm
        movew           %d1,ETEMP(%a6)  //input expected in ETEMP
        movel           FPTEMP_HI(%a6),ETEMP_HI(%a6)
        movel           FPTEMP_LO(%a6),ETEMP_LO(%a6)
        orl             #unfl_bit,USER_FPSR(%a6)        //set unfl
        leal            ETEMP(%a6),%a0
        bra             t_resdnrm
nden_exit:
        movew           %d1,FPTEMP(%a6) //result in FPTEMP
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0        //write result to fp0
        rts

//
// Source is negative.  Add the src to the dest exponent.
// (The result exponent will be reduced).  The result can be
// denormalized.
//
src_neg:
        addl            %d0,%d1         //add src to dest
        beqs            denorm          //if zero, result is denorm
        blts            fix_dnrm        //if negative, result is 
//                                      ;needing denormalization
        tstb            L_SCR1(%a6)
        beqs            sneg_pos
        orw             #0x8000,%d1
sneg_pos:
        movew           %d1,FPTEMP(%a6) //result in FPTEMP
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0        //write result to fp0
        rts


//
// The result exponent is below denorm value.  Test for catastrophic
// underflow and force zero if true.  If not, try to shift the 
// mantissa right until a zero exponent exists.
//
fix_dnrm:
        cmpiw           #0xffc0,%d1     //lower bound for normalization
        blt             fix_unfl        //if lower, catastrophic unfl
        movew           %d1,%d0         //use d0 for exp
        movel           %d2,-(%a7)      //free d2 for norm
        movel           FPTEMP_HI(%a6),%d1
        movel           FPTEMP_LO(%a6),%d2
        clrl            L_SCR2(%a6)
fix_loop:
        addw            #1,%d0          //drive d0 to 0
        lsrl            #1,%d1          //while shifting the
        roxrl           #1,%d2          //mantissa to the right
        bccs            no_carry
        st              L_SCR2(%a6)     //use L_SCR2 to capture inex
no_carry:
        tstw            %d0             //it is finished when
        blts            fix_loop        //d0 is zero or the mantissa
        tstb            L_SCR2(%a6)
        beqs            tst_zero
        orl             #unfl_inx_mask,USER_FPSR(%a6)
//                                      ;set unfl, aunfl, ainex
//
// Test for zero. If zero, simply use fmove to return +/- zero
// to the fpu.
//
tst_zero:
        clrw            FPTEMP_EX(%a6)
        tstb            L_SCR1(%a6)     //test for sign
        beqs            tst_con
        orw             #0x8000,FPTEMP_EX(%a6) //set sign bit
tst_con:
        movel           %d1,FPTEMP_HI(%a6)
        movel           %d2,FPTEMP_LO(%a6)
        movel           (%a7)+,%d2
        tstl            %d1
        bnes            not_zero
        tstl            FPTEMP_LO(%a6)
        bnes            not_zero
//
// Result is zero.  Check for rounding mode to set lsb.  If the
// mode is rp, and the zero is positive, return smallest denorm.
// If the mode is rm, and the zero is negative, return smallest
// negative denorm.
//
        btstb           #5,FPCR_MODE(%a6) //test if rm or rp
        beqs            no_dir
        btstb           #4,FPCR_MODE(%a6) //check which one
        beqs            zer_rm
zer_rp:
        tstb            L_SCR1(%a6)     //check sign
        bnes            no_dir          //if set, neg op, no inc
        movel           #1,FPTEMP_LO(%a6) //set lsb
        bras            sm_dnrm
zer_rm:
        tstb            L_SCR1(%a6)     //check sign
        beqs            no_dir          //if clr, neg op, no inc
        movel           #1,FPTEMP_LO(%a6) //set lsb
        orl             #neg_mask,USER_FPSR(%a6) //set N
        bras            sm_dnrm
no_dir:
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0        //use fmove to set cc's
        rts

//
// The rounding mode changed the zero to a smallest denorm. Call 
// t_resdnrm with exceptional operand in ETEMP.
//
sm_dnrm:
        movel           FPTEMP_EX(%a6),ETEMP_EX(%a6)
        movel           FPTEMP_HI(%a6),ETEMP_HI(%a6)
        movel           FPTEMP_LO(%a6),ETEMP_LO(%a6)
        leal            ETEMP(%a6),%a0
        bra             t_resdnrm

//
// Result is still denormalized.
//
not_zero:
        orl             #unfl_mask,USER_FPSR(%a6) //set unfl
        tstb            L_SCR1(%a6)     //check for sign
        beqs            fix_exit
        orl             #neg_mask,USER_FPSR(%a6) //set N
fix_exit:
        bras            sm_dnrm

        
//
// The result has underflowed to zero. Return zero and set
// unfl, aunfl, and ainex.
//
fix_unfl:
        orl             #unfl_inx_mask,USER_FPSR(%a6)
        btstb           #5,FPCR_MODE(%a6) //test if rm or rp
        beqs            no_dir2
        btstb           #4,FPCR_MODE(%a6) //check which one
        beqs            zer_rm2
zer_rp2:
        tstb            L_SCR1(%a6)     //check sign
        bnes            no_dir2         //if set, neg op, no inc
        clrl            FPTEMP_EX(%a6)
        clrl            FPTEMP_HI(%a6)
        movel           #1,FPTEMP_LO(%a6) //set lsb
        bras            sm_dnrm         //return smallest denorm
zer_rm2:
        tstb            L_SCR1(%a6)     //check sign
        beqs            no_dir2         //if clr, neg op, no inc
        movew           #0x8000,FPTEMP_EX(%a6)
        clrl            FPTEMP_HI(%a6)
        movel           #1,FPTEMP_LO(%a6) //set lsb
        orl             #neg_mask,USER_FPSR(%a6) //set N
        bra             sm_dnrm         //return smallest denorm

no_dir2:
        tstb            L_SCR1(%a6)
        bges            pos_zero
neg_zero:
        clrl            FP_SCR1(%a6)    //clear the exceptional operand
        clrl            FP_SCR1+4(%a6)  //for gen_except.
        clrl            FP_SCR1+8(%a6)
        fmoves          #0x80000000,%fp0        
        rts
pos_zero:
        clrl            FP_SCR1(%a6)    //clear the exceptional operand
        clrl            FP_SCR1+4(%a6)  //for gen_except.
        clrl            FP_SCR1+8(%a6)
        fmoves          #0x00000000,%fp0
        rts

//
// The destination is a denormalized number.  It must be handled
// by first shifting the bits in the mantissa until it is normalized,
// then adding the remainder of the source to the exponent.
//
dst_dnrm:
        moveml          %d2/%d3,-(%a7)  
        movew           FPTEMP_EX(%a6),%d1
        movel           FPTEMP_HI(%a6),%d2
        movel           FPTEMP_LO(%a6),%d3
dst_loop:
        tstl            %d2             //test for normalized result
        blts            dst_norm        //exit loop if so
        tstl            %d0             //otherwise, test shift count
        beqs            dst_fin         //if zero, shifting is done
        subil           #1,%d0          //dec src
        lsll            #1,%d3
        roxll           #1,%d2
        bras            dst_loop
//
// Destination became normalized.  Simply add the remaining 
// portion of the src to the exponent.
//
dst_norm:
        addw            %d0,%d1         //dst is normalized; add src
        tstb            L_SCR1(%a6)
        beqs            dnrm_pos
        orl             #0x8000,%d1
dnrm_pos:
        movemw          %d1,FPTEMP_EX(%a6)
        moveml          %d2,FPTEMP_HI(%a6)
        moveml          %d3,FPTEMP_LO(%a6)
        fmovel          USER_FPCR(%a6),%FPCR
        fmovex          FPTEMP(%a6),%fp0
        moveml          (%a7)+,%d2/%d3
        rts

//
// Destination remained denormalized.  Call t_excdnrm with
// exceptional operand in ETEMP.
//
dst_fin:
        tstb            L_SCR1(%a6)     //check for sign
        beqs            dst_exit
        orl             #neg_mask,USER_FPSR(%a6) //set N
        orl             #0x8000,%d1
dst_exit:
        movemw          %d1,ETEMP_EX(%a6)
        moveml          %d2,ETEMP_HI(%a6)
        moveml          %d3,ETEMP_LO(%a6)
        orl             #unfl_mask,USER_FPSR(%a6) //set unfl
        moveml          (%a7)+,%d2/%d3
        leal            ETEMP(%a6),%a0
        bra             t_resdnrm

//
// Source is outside of 2^14 range.  Test the sign and branch
// to the appropriate exception handler.
//
src_out:
        tstb            L_SCR1(%a6)
        beqs            scro_pos
        orl             #0x8000,%d1
scro_pos:
        movel           FPTEMP_HI(%a6),ETEMP_HI(%a6)
        movel           FPTEMP_LO(%a6),ETEMP_LO(%a6)
        tstw            ETEMP(%a6)
        blts            res_neg
res_pos:
        movew           %d1,ETEMP(%a6)  //result in ETEMP
        bra             t_ovfl2
res_neg:
        movew           %d1,ETEMP(%a6)  //result in ETEMP
        leal            ETEMP(%a6),%a0
        bra             t_unfl
        |end