//
// $Id$
//
// 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// THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA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
